Method for making a sintered superhard prosthetic joint component

ABSTRACT

Use of Ti and Nb cemented in TiC in prosthetic joints, such as prosthetic joint components made from sintered superhard materials.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 10/259,187 filed on Sep. 28, 2002, now abandoned,which is a continuation-in-part of U.S. patent application Ser. No.10/229,907 filed on Aug. 28, 2002 now U.S. Pat No. 7,494,507, (whichclaims priority U.S. Provisional Patent Application Ser. No. 60/325,832filed on Sep. 28, 2001, now abandoned). This patent application is acontinuation-in-part of U.S. patent application Ser. No. 09/494,276filed on Jan. 30, 2000, now U.S. Pat. No. 6,793,681, and priority isclaimed to all of the foregoing.

This patent application claims priority to U.S. Provisional PatentApplication Ser. 60/499,026 filed on Aug. 29, 2003; to U.S. ProvisionalPatent Application Ser. No. 60/498,768 filed on Aug. 29, 2003; to U.S.Provisional Patent Application Ser. No. 60/498,968 filed on Aug. 29,2003, to U.S. Provisional Patent Application Ser. No. 60/498,709 filedon Aug. 28, 2003, to U.S. Provisional Patent Application Ser. No.60/498,896 filed on Aug. 29, 2003 and to U.S. Provisional PatentApplication Ser. No. 60/498,708 filed on Aug. 28, 2003. Each of theforegoing is hereby incorporated by reference.

BACKGROUND

This disclosure relates to methods, materials and apparatuses for makingsuperhard (i.e., polycrystalline diamond and polycrystalline cubic boronnitride) components, and other hard components.

SUMMARY

Various methods, materials and apparatuses for making superhardcomponents and other hard components are disclosed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A depicts a quantity of diamond feedstock adjacent to a metalalloy substrate prior to sintering of the diamond feedstock and thesubstrate to create a PDC.

FIG. 1B depicts a sintered PDC in which the diamond table, thesubstrate, and the transition zone between the diamond table and thesubstrate are shown.

FIG. 1 BB depicts a sintered PDC in which there is a continuous gradienttransition from substrate metal through the diamond table.

FIG. 1C depicts a substrate prior to use of a CVD or PVD process to forma volume of diamond on the substrate.

FIG. 1D depicts a diamond compact formed by a CVD or PVD process.

FIG. 1E depicts a device, which may be used for loading diamondfeedstock prior to sintering.

FIG. 1F depicts a furnace cycle for removal of a binder material fromdiamond feedstock prior to sintering.

FIGS. 1G and 1GA depict a precompaction assembly, which may be used toreduce free space in diamond feedstock prior to sintering.

FIG. 2 depicts the anvils of a cubic press that can be used to provide ahigh temperature and high pressure sintering environment, or forhipping.

FIGS. 3A-1 through 3A-11 depict controlling large volumes of powderfeedstocks, such as diamond.

FIGS. 4A-4I1 depict some example superhard constructs.

FIGS. 5-12 depict preparation of superhard materials for use in makingan articulating diamond-surfaced spinal implant component.

FIGS. 13A-13G depict some substrate and superhard materialconfigurations.

FIGS. 14-36 depict superhard material preparation before sintering andremoval after sintering.

FIGS. 37 a-37 c depict sintering of arcuate superhard surfaces.

FIGS. 38-50 depict machining and finishing superhard articulatingdiamond-surfaced spinal implant components.

DETAILED DESCRIPTION

Reference will now be made to the drawings in which the various elementsof the embodiments will be discussed. Persons skilled in the design ofprosthetic joints and other bearing surfaces will understand theapplication of the various embodiments and their principles to sinteringand hipping of superhard and hard components, including those used inprosthetic joints of all types, and components of prosthetic joints,anywhere hard, durable or biocompatabile products are desired, and fordevices other than those exemplified herein.

Various embodiments of the manufacturing systems, devices, processes andmaterials disclosed herein relate to superhard and hard surfaces andcomponents. More specifically, some relate to diamond and sinteredpolycrystalline diamond surfaces (PCD). Some embodiments make or utilizea polycrystalline diamond compact (PDC) to provide a very strong, lowfriction, long-wearing, biocompatible part or surface. Any surface ordevices that experiences wear and requires strength and durability willbenefit from the advances made here.

The table below provides a comparison of sintered PCD to some othermaterials.

TABLE 1 COMPARISON OF SINTERED PCD TO OTHER MATERIALS Coefficient ofThermal Thermal Expansion Specific Hardness Conductivity (“CTE”)Material Gravity (Knoop) (W/m K) (×10⁻⁶) Sintered 3.5-4.0 9000 9001.50-4.8  Polycrystalline Diamond Compact (PDC) Cubic Boron 3.48 4500800 1.0-4.0 Nitride Silicon 3.00 2500 84 4.7-5.3 Carbide Aluminum 3.502000 7.8-8.8 Oxide Tungsten 14.6 2200 112 4-6 Carbide (10% Co) Cobalt8.2 43 RC 16.9 Chrome Ti6Al4V 4.43 6.6-17.5 11 Silicon Nitride 3.2 14.215-7  1.8-3.7

In view of the superior hardness of sintered PCD, it is expected thatsintered PCD will provide improved wear and durability characteristics.

In a PDC, the diamond table is chemically bonded and mechanically fixedto the substrate in a manufacturing process that typically uses acombination of high pressure and high temperature to form the sinteredPCD (see, infra).

The chemical bonds between the diamond table and the substrate areestablished during the sintering process by combinations of unsatisfiedsp3 carbon bonds with unsatisfied substrate metal bonds. The mechanicalfixation is a result of shape of the substrate and diamond table anddifferences in the physical properties of the substrate and the diamondtable as well as the gradient interface between the substrate and thediamond table. The resulting sintered PDC forms a durable modularbearing inserts and joints.

The diamond table may be polished to a very smooth and glass-like finishto achieve a very low coefficient of friction. The high surface energyof sintered PDC causes it to work very well as a load-bearing andarticulation surface when a lubricating fluid is present. Its inherentnature allows it to perform very well when a lubricant is absent aswell.

While there is discussion herein concerning PDCs, the followingmaterials could be considered for forming prosthetic joint components:polycrystalline diamond, monocrystal diamond, natural diamond, diamondcreated by physical vapor deposition, diamond created by chemical vapordeposition, diamond like carbon, carbonado, cubic boron nitride,hexagonal boron nitride, or a combination of these, cobalt, chromium,titanium, vanadium, stainless steel, niobium, aluminum, nickel, hafnium,silicon, tungsten, molybdenum, aluminum, zirconium, nitinol, cobaltchrome, cobalt chrome molybdenum, cobalt chrome tungsten, tungstencarbide, titanium carbide, tantalum carbide, zirconium carbide, hafniumcarbide, Ti6/4, silicon carbide, chrome carbide, vanadium carbide,yttria stabilized zirconia, magnesia stabilized zirconia, zirconiatoughened alumina, titanium molybdenum hafnium, alloys including one ormore of the above metals, ceramics, quartz, garnet, sapphire,combinations of these materials, combinations of these and othermaterials, and other materials may also be used for a desired surface.

Sintered Polycrystalline Diamond Compacts

One useful material for manufacturing joint bearing surfaces is asintered polycrystalline diamond compact. Diamond has the greatesthardness and the lowest coefficient of friction of any currently knownmaterial. Sintered PDCs are chemically inert, are impervious to allsolvents, and have the highest thermal conductivity at room temperatureof any known material.

In some embodiments, a PDC provides unique chemical bonding andmechanical grip between the diamond and the substrate material. A PDC,which utilizes a substrate material, will have a chemical bond betweensubstrate material and the diamond crystals. The result of thisstructure is an extremely strong bond between the substrate and thediamond table.

A method by which PDC may be manufactured is described later in thisdocument. Briefly, it involves sintering diamond crystals to each other,and to a substrate under high pressure and high temperature. FIGS. 1Aand 1B illustrate the physical and chemical processes involvedmanufacturing PDCs.

In FIG. 1A, a quantity of diamond feedstock 130 (such as diamond powderor crystals) is placed adjacent to a metal-containing substrate 110prior to sintering. In the region of the diamond feedstock 130,individual diamond crystals 131 may be seen, and between the individualdiamond crystals 131 there are interstitial spaces 132. If desired, aquantity of solvent-catalyst metal may be placed into the interstitialspaces 132. The substrate may also contain solvent-catalyst metal.

The substrate 110 may be a suitable pure metal or alloy, or a cementedcarbide containing a suitable metal or alloy as a cementing agent suchas cobalt-cemented tungsten carbide or other materials mentioned herein.The substrate 110 may be a metal with high tensile strength. In acobalt-chrome substrate, the cobalt-chrome alloy will serve as asolvent-catalyst metal for solvating diamond crystals during thesintering process.

The illustration shows the individual diamond crystals and thecontiguous metal crystals in the metal substrate. The interface 120between diamond powder and substrate material is a region where bondingof the diamond table to the substrate must occur. In some embodiments, aboundary layer of a third material different than the diamond and thesubstrate is placed at the interface 120. This interface boundary layermaterial, when present, may serve several functions including, but notlimited to, enhancing the bond of the diamond table to the substrate,and mitigation of the residual stress field at the diamond-substrateinterface.

Once diamond powder or crystals and substrate are assembled as shown inFIG. 1A, the assembly is subjected to high pressure and high temperatureas described later herein in order to cause bonding of diamond crystalsto diamond crystals and to the substrate. The resulting structure ofsintered polycrystalline diamond table bonded to a substrate is called apolycrystalline diamond compact or a PDC. A compact, as the term is usedherein, is a composite structure of two different materials, such asdiamond crystals, and a substrate metal. The analogous structureincorporating cubic boron nitride crystals in the sintering processinstead of diamond crystals is called polycrystalline cubic boronnitride compact (PCBNC). Many of the processes described herein for thefabrication and finishing of PDC structures and parts work in a similarfashion for PCBNC. In some embodiments, PCBNC may be substituted forPDC. It should be noted that a PDC can also be made from free standingdiamond without a separate substrate, as described elsewhere herein.

FIG. 1B depicts a PDC 101 after the high pressure and high temperaturesintering of diamond feedstock to a substrate. Within the PDC structure,there is an identifiable volume of substrate 102, an identifiable volumeof diamond table 103, and a transition zone 104 between diamond tableand substrate containing diamond crystals and substrate material.Crystalline grains of substrate material 105 and sintered crystals ofdiamond 106 are depicted.

On casual examination, the finished compact of FIG. 1B will appear toconsist of a solid table of diamond 103 attached to the substrate 102with a discrete boundary. On very close examination, however, atransition zone 104 between diamond table 103 and substrate 102 can becharacterized. This zone represents a gradient interface between diamondtable and substrate with a gradual transition of ratios between diamondcontent and metal content. At the substrate side of the transition zone,there will be only a small percentage of diamond crystals and a highpercentage of substrate metal, and on the diamond table side, there willbe a high percentage of diamond crystals and a low percentage ofsubstrate metal. Because of this gradual transition of ratios ofpolycrystalline diamond to substrate metal in the transition zone, thediamond table and the substrate have a gradient interface.

In the transition zone or gradient transition zone where diamondcrystals and substrate metal are intermingled, chemical bonds are formedbetween the diamond and metal. From the transition zone 104 into thediamond table 103, the metal content diminishes and is limited tosolvent-catalyst metal that fills the three-dimensional vein-likestructure of interstitial voids, openings or asperities 107 within thesintered diamond table structure 103. The solvent-catalyst metal foundin the voids or openings 107 may have been swept up from the substrateduring sintering or may have been solvent-catalyst metal added to thediamond feedstock before sintering.

During the sintering process, there are three types of chemical bondsthat are created: diamond-to-diamond bonds, diamond-to-metal bonds, andmetal-to-metal bonds. In the diamond table, there are diamond-to-diamondbonds (sp3 carbon bonds) created when diamond particles partiallysolvate in the solvate-catalyst metal and then are bonded together. Inthe substrate and in the diamond table, there are metal-to-metal bondscreated by the high pressure and high temperature sintering process. Andin the gradient transition zone, diamond-to-metal bonds are createdbetween diamond and solvent-catalyst metal.

The combination of these various chemical bonds and the mechanical gripexerted by solvent-catalyst metal in the diamond table such as in theinterstitial spaces of the diamond structure diamond table provideextraordinarily high bond strength between the diamond table and thesubstrate. Interstitial spaces are present in the diamond structure andthose spaces typically are filled with solvent-catalyst metal, formingveins of solvent-catalyst metal within the polycrystalline diamondstructure. This bonding structure contributes to the extraordinaryfracture toughness of the compact, and the veins of metal within thediamond table act as energy sinks halting propagation of incipientcracks within the diamond structure. The transition zone and metal veinstructure provide the compact with a gradient of material propertiesbetween those of the diamond table and those of substrate material,further contributing to the extreme toughness of the compact. Thetransition zone can also be called an interface, a gradient transitionzone, a composition gradient zone, or a composition gradient, dependingon its characteristics. The transition zone distributesdiamond/substrate stress over the thickness of the zone, reducing zonehigh stress of a distinct linear interface. The subject residual stressis created as pressure and temperature are reduced at the conclusion ofthe high pressure/high temperature sintering process due to thedifference in pressure and thermal expansive properties of the diamondand substrate materials.

The diamond sintering process occurs under conditions of extremely highpressure and high temperature. According to the inventors' bestexperimental and theoretical understanding, the diamond sinteringprocess progresses through the following sequence of events: Atpressure, a cell containing feedstock of unbonded diamond powder orcrystals (diamond feedstock) and a substrate is heated to a temperatureabove the melting point of the substrate metal 110 and molten metalflows or sweeps into the interstitial voids 107 between the adjacentdiamond crystals 106. It is carried by the pressure gradient to fill thevoids as well as being pulled in by the surface energy or capillaryaction of the large surface area of the diamond crystals 106. As thetemperature continues to rise, carbon atoms from the surface of diamondcrystals dissolve into this interstitial molten metal, forming a carbonsolution.

At the proper threshold of temperature and pressure, diamond becomes thethermodynamically favored crystalline allotrope of carbon. As thesolution becomes super saturated with respect to C_(d) (carbon diamond),carbon from this solution begins to crystallize as diamond onto thesurfaces of diamond crystals bonding adjacent diamond crystals togetherwith diamond-diamond bonds into a sintered polycrystalline diamondstructure 106. The interstitial metal fills the remaining void spaceforming the vein-like lattice structure 107 within the diamond table bycapillary forces and pressure driving forces. Because of the crucialrole that the interstitial metal plays in forming a solution of carbonatoms and stabilizing these reactive atoms during the diamondcrystallization phase in which the polycrystalline diamond structure 106is formed, the metal is referred to as a solvent-catalyst metal.

FIG. 1 BB depicts a polycrystalline diamond compact having bothsubstrate metal 180 and diamond 181, but in which there is a continuousgradient transition 182 from substrate metal to diamond. In such acompact, the gradient transition zone may be the entire compact, or aportion of the compact. The substrate side of the compact may containnearly pure metal for easy machining and attachment to other components,while the diamond side may be extremely hard, smooth and durable for usein a hostile work environment.

In some embodiments, a quantity of solvent-catalyst metal may becombined with the diamond feedstock prior to sintering. This is found tobe necessary when forming thick PCD tables, solid PDC structures, orwhen using multimodal fine diamond where there is little residual freespace within the diamond powder. In each of these cases, there may notbe sufficient ingress of solvent-catalyst metal via the sweep mechanismto adequately mediate the sintering process as a solvent-catalyst. Themetal may be added by direct addition of powder, or by generation ofmetal powder in situ with an attritor mill or by the well-known methodof chemical reduction of metal salts deposited on diamond crystals.Added metal may constitute any amount from less than 1% by mass, togreater than 35%. This added metal may consist of the same metal oralloy as is found in the substrate, or may be a different metal or alloyselected because of its material and mechanical properties. Exampleratios of diamond feedstock to solvent-catalyst metal prior to sinteringinclude mass ratios of 70:30, 85:15, 90:10, and 95:15. The metal in thediamond feedstock may be added powder metal, metal added by an attritormethod, vapor deposition or chemical reduction of metal into powder.

When sintering diamond on a substrate with an interface boundary layer,it may be that no solvent-catalyst metal from the substrate is availableto sweep into the diamond table and participate in the sinteringprocess. In this case, the boundary layer material, if composed of asuitable material, metal or alloy that can function as asolvent-catalyst, may serve as the sweep material mediating the diamondsintering process. In other cases where the desired boundary materialcannot serve as a solvent-catalyst, a suitable amount ofsolvent-catalyst metal powder as described herein is added to thediamond crystal feed stock as described above. This assembly is thentaken through the sintering process. In the absence of a substrate metalsource, the solvent-catalyst metal for the diamond sintering processmust be supplied entirely from the added metal powder. The boundarymaterial may bond chemically to the substrate material, and may bondchemically to the diamond table and/or the added solvent-catalyst metalin the diamond table. The remainder of the sintering and fabricationprocess may be the same as with the conventional solvent-catalyst sweepsintering and fabrication process.

For the sake of simplicity and clarity in this patent, the substrate,transition zone, and diamond table have been discussed as distinctlayers. However, it is important to realize that the finished sinteredobject may be a composite structure characterized by a continuousgradient transition from substrate material to diamond table rather thanas distinct layers with clear and discrete boundaries, hence the term“compact.”

In addition to the sintering processes described above, diamond partssuitable for use as modular bearing inserts and joint components mayalso be fabricated as solid or free-standing polycrystalline diamondstructures without a substrate. These may be formed by placing thediamond powder combined with a suitable amount of added solvent-catalystmetal powder as described above in a refractory metal can (typically Ta,Nb, Zr, or Mo) with a shape approximating the shape of the final partdesired. This assembly is then taken through the sintering process.However, in the absence of a substrate metal source, thesolvent-catalyst metal for the diamond sintering process must besupplied entirely from the added metal powder. With suitable finishing,objects thus formed may be used as is, or bonded to metal or othersubstrates.

Sintering is a method of creating a diamond table with a strong anddurable constitution. Other methods of producing a diamond table thatmay or may not be bonded to a substrate are possible. At present, thesetypically are not as strong or durable as those fabricated with thesintering process. It is also possible to use these methods to formdiamond structures directly onto substrates suitable for use as modularbearing inserts and joints. A table of polycrystalline diamond eitherwith or without a substrate may be manufactured and later attached to amodular bearing inserts and joints in a location such that it will forma surface. The attachment could be performed with any suitable method,including welding, brazing, sintering, diffusion welding, diffusionbonding, inertial welding, adhesive bonding, or the use of fastenerssuch as screws, bolts, or rivets. In the case of attaching a diamondtable without a substrate to another object, the use of such methods asbrazing, diffusion welding/bonding or inertia welding may be mostappropriate.

Although high pressure/high temperature sintering is a method forcreating a diamond surface, other methods for producing a volume ofdiamond may be employed as well. For example, either chemical vapordeposition (CVD), or physical vapor deposition (PVD) processes may beused. CVD produces a diamond layer by thermally cracking an organicmolecule and depositing carbon radicals on a substrate. PVD produces adiamond layer by electrically causing carbon radicals to be ejected froma source material and to deposit on a substrate where they build adiamond crystal structure.

The CVD and PVD processes have some advantages over sintering. Sinteringis performed in large, expensive presses at high pressure (such as 45-68kilobars) and at high temperatures (such as 1200 to 1500 degreesCelsius). It is difficult to achieve and maintain desired componentshape using a sintering process because of flow of high pressure mediumsused and possible deformation of substrate materials.

In contrast, CVD and PVD take place at atmospheric pressure or lower, sothere no need for a pressure medium and there is no deformation ofsubstrates.

Another disadvantage of sintering is that it is difficult to achievesome geometries in a sintered PDC. When CVD or PVD are used, however,the gas phase used for carbon radical deposition can completely conformto the shape of the object being coated, making it easy to achieve adesired non-planar shape.

Another potential disadvantage of sintering PDCs is that the finishedcomponent will tend to have large residual stresses caused bydifferences in the coefficient of thermal expansion and modulus betweenthe diamond and the substrate. While residual stresses can be used toimprove strength of a part, they can also be disadvantageous. When CVDor PVD is used, residual stresses can be minimized because CVD and PVDprocesses do not involve a significant pressure transition (such from 68Kbar to atmospheric pressure in high pressure and high temperaturesintering) during manufacturing.

Another potential disadvantage of sintering PDCs is that few substrateshave been found that are suitable for sintering. Tungsten carbide is acommon choice for substrate materials. Non-planar components have beenmade using other substrates. When CVD or PVD are used, however,synthetic diamond can be placed on many substrates, including titanium,most carbides, silicon, molybdenum and others. This is because thetemperature and pressure of the CVD and PVD coating processes are lowenough that differences in coefficient of thermal expansion and modulusbetween diamond and the substrate are not as critical as they are in ahigh temperature and high pressure sintering process.

A further difficulty in manufacturing sintered PDCs is that as the sizeof the part to be manufactured increases, the size of the press mustincrease as well. Sintering of diamond will only take place at certainpressures and temperatures, such as those described herein. In order tomanufacture larger sintered polycrystalline diamond compacts, rampressure of the press (tonnage) and size of tooling (such as dies andanvils) must be increased in order to achieve the necessary pressure forsintering to take place. But increasing the size and capacity of a pressis more difficult than simply increasing the dimensions of itscomponents. There may be practical physical size constraints on presssize due to the manufacturing process used to produce press tooling.

Tooling for a press is typically made from cemented tungsten carbide. Inorder to make tooling, the cemented tungsten carbide is sintered in avacuum furnace followed by pressing in a hot isosatic press (“HIP”)apparatus. Hipping should be performed in a manner that maintainsuniform temperature throughout the tungsten carbide in order to achieveuniform physical qualities and quality. These requirements impose apractical limit on the size tooling that can be produced for a pressthat is useful for sintering PDCs. The limit on the size tooling thatcan be produced also limits the size press that can be produced.

CVD and PVD manufacturing apparatuses may be scaled up in size with fewlimitations, allowing them to produce polycrystalline diamond compactsof almost any desired size.

CVD and PVD processes are also advantageous because they permit precisecontrol of the thickness and uniformity of the diamond coating to beapplied to a substrate. Temperature is adjusted within the range of 500to 1000 degrees Celsius, and pressure is adjusted in a range of lessthan 1 atmosphere to achieve desired diamond coating thickness.

Another advantage of CVD and PVD processes is that they allow themanufacturing process to be monitored as it progresses. A CVD or PVDreactor can be opened before manufacture of a part is completed so thatthe thickness and quality of the diamond coating being applied to thepart may be determined. From the thickness of the diamond coating thathas already been applied, time to completion of manufacture can becalculated. Alternatively, if the coating is not of desired quality, themanufacturing processes may be aborted in order to save time and money.

In contrast, sintering of PDCs is performed as a batch process thatcannot be interrupted, and progress of sintering cannot be monitored.The pressing process must be run to completion and the part may only beexamined afterward.

A cubic press (i.e., the press has six anvil faces) may be used fortransmitting high pressure to an assembly to under sintering or hipping.For example, a cubic press applies pressure along 3 axes from sixdifferent directions. Alternatively, a belt press and a cylindrical cellcan be used to obtain similar results. Other presses that may be usedinclude a piston-cylinder press and a tetrahedral press. Referring toFIG. 2, a representation of the 6 anvils of a cubic press 3720 isprovided. The anvils 3721, 3722, 3723, 3724, 3725 and 3726 are situatedaround a pressure assembly 3730 to carry out sintering or hipping by useof high temperature and high pressure. The exact sintering or hippingconditions depend on the materials used, size of the component beingmanufactured, and the material and strength properties desired in thefinished product.

A cubic press usually relies on six carbide anvils attached to massivehydraulic cylinders converging simultaneously on a cube-shapedhigh-pressure capsule. This tri-axial system generates an essentiallyiso-static high-pressure condition, which is particularly suited tosintering products with complex 3-dimensional geometries. Such a presssystem will be integrated with computerized control systems to assureoptimal and consistent pressure, time, and temperature sinteringconditions.

A belt press uses two carbide punches converging upon a high-pressurecapsule contained within a carbide die to generate the extreme pressurerequired to sinter polycrystalline products. Shrink-fitted steel beltspre-stress the inner carbide die, allowing it to withstand the immenseinternal pressure that occurs during sintering.

A piston-cylinder press is similar to a belt press, with a high-pressurecapsule is contained within the cylindrical bore of a carbide die. Twofree-floating carbide pistons engage within the bore, pressurizing thecapsule when load is applied by conical carbide anvils. The carbide dieis supported by radial hydraulic pressure rather than a series of steelbelts. This allows simultaneous pressurization of both the inside andoutside of the die. Since this press is essentially a gasketless system,there is very little material movement within the pressure volume duringpressurization and heating.

CVD and PVD Diamond

CVD is performed in an apparatus called a reactor. A basic CVD reactorincludes four components. The first component of the reactor is one ormore gas inlets. Gas inlets may be chosen based on whether gases arepremixed before introduction to the chamber or whether the gases areallowed to mix for the first time in the chamber. The second componentof the reactor is one or more power sources for the generation ofthermal energy. A power source is needed to heat the gases in thechamber. A second power source may be used to heat the substratematerial uniformly in order to achieve a uniform coating of diamond onthe substrate. The third component of the reactor is a stage or platformon which a substrate is placed. The substrate will be coated withdiamond during the CVD process. Stages used include a fixed stage, atranslating stage, a rotating stage and a vibratory stage. Anappropriate stage must be chosen to achieve desired diamond coatingquality and uniformity. The fourth component of the reactor is an exitport for removing exhaust gas from the chamber. After gas has reactedwith the substrate, it must be removed from the chamber as quickly aspossible so that it does not participate in other reactions, which wouldbe deleterious to the diamond coating.

CVD reactors are classified according to the power source used. Thepower source is chosen to create the desired species necessary to carryout diamond thin film deposition. Some CVD reactor types includeplasma-assisted microwave, hot filament, electron beam, single, doubleor multiple laser beam, arc jet and DC discharge. These reactors differin the way they impart thermal energy to the gas species and in theirefficiency in breaking gases down to the species necessary fordeposition of diamond. It is possible to have an array of lasers toperform local heating inside a high pressure cell. Alternatively, anarray of optical fibers could be used to deliver light into the cell.

The basic process by which CVD reactors work is as follows. A substrateis placed into the reactor chamber. Reactants are introduced to thechamber via one or more gas inlets. For diamond CVD, methane (CH₄) andhydrogen (H₂) gases may be brought into the chamber in premixed form.Instead of methane, any carbon-bearing gas in which the carbon has sp3bonding may be used. Other gases may be added to the gas stream in orderto control quality of the diamond film, deposition temperature, gainstructure and growth rate. These include oxygen, carbon dioxide, argon,halogens and others.

The gas pressure in the chamber is maintained at about 100 torr. Flowrates for the gases through the chamber are about 10 standard cubiccentimeters per minute for methane and about 100 standard cubiccentimeters per minute for hydrogen. The composition of the gas phase inthe chamber is in the range of 90-99.5% hydrogen and 0.5-10% methane.

When the gases are introduced into the chamber, they are heated. Heatingmay be accomplished by many methods. In a plasma-assisted process, thegases are heated by passing them through a plasma. Otherwise, the gasesmay be passed over a series of wires such as those found in a hotfilament reactor.

Heating the methane and hydrogen will break them down into various freeradicals. Through a complicated mixture of reactions, carbon isdeposited on the substrate and joins with other carbon to formcrystalline diamond by sp3 bonding. The atomic hydrogen in the chamberreacts with and removes hydrogen atoms from methyl radicals attached tothe substrate surface in order to create molecular hydrogen, leaving aclear solid surface for further deposition of free radicals.

If the substrate surface promotes the formation of sp2 carbon bonds, orif the gas composition, flow rates, substrate temperature or othervariables are incorrect, then graphite rather than diamond will grow onthe substrate.

There are many similarities between CVD reactors and processes and PVDreactors and processes. PVD reactors differ from CVD reactors in the waythat they generate the deposition species and in the physicalcharacteristics of the deposition species. In a PVD reactor, a plate ofsource material is used as a thermal source, rather than having aseparate thermal source as in CVD reactors. A PVD reactor generateselectrical bias across a plate of source material in order to generateand eject carbon radicals from the source material. The reactor bombardsthe source material with high energy ions. When the high energy ionscollide with source material, they cause ejection of the desired carbonradicals from the source material. The carbon radicals are ejectedradially from the source material into the chamber. The carbon radicalsthen deposit themselves onto whatever is in their path, including thestage, the reactor itself, and the substrate.

Referring to FIG. 1C, a substrate 140 of appropriate material isdepicted having a deposition face 141 on which diamond may be depositedby a CVD or PVD process. FIG. 1D depicts the substrate 140 and thedeposition face 141 on which a volume of diamond 142 has been depositedby CVD or PVD processes. A small transition zone 143 is present in whichboth diamond and substrate are located. In comparison to FIG. 1B, it canbe seen that the CVD or PVD diamond deposited on a substrate lacks themore extensive gradient transition zone of sintered polycrystallinediamond compacts because there is no sweep of solvent-catalyst metalthrough the diamond table in a CVD or PVD process.

Both CVD and PVD processes achieve diamond deposition by line of sight.Means (such as vibration and rotation) are provided for exposing alldesired surfaces for diamond deposition. If a vibratory stage is to beused, the surface will vibrate up and down with the stage and therebypresent all surfaces to the free radical source.

There are several methods, which may be implemented in order to coatcylindrical objects with diamond using CVD or PVD processes. If a plasmaassisted microwave process is to be used to achieve diamond deposition,then the object to receive the diamond must be directly under the plasmain order to achieve the highest quality and most uniform coating ofdiamond. A rotating or translational stage may be used to present everyaspect of the surface to the plasma for diamond coating. As the stagerotates or translates, all portions of the surface may be broughtdirectly under the plasma for coating in such a way to achievesufficiently uniform coating.

If a hot filament CVD process is used, then the surface should be placedon a stationary stage. Wires or filaments (typically tungsten) arestrung over the stage so that their coverage includes the surface to becoated. The distance between the filaments and the surface and thedistance between the filaments themselves may be chosen to achieve auniform coating of diamond directly under the filaments.

Diamond surfaces can be manufactured by CVD and PVD process either bycoating a substrate with diamond or by creating a free-standing volumeof diamond, which is later mounted for use. A free-standing volume ofdiamond may be created by CVD and PVD processes in a two-step operation.First, a thick film of diamond is deposited on a suitable substrate,such as silicon, molybdenum, tungsten or others. Second, the diamondfilm is released from the substrate.

As desired, segments of diamond film may be cut away, such as by use ofa Q-switched YAG laser. Although diamond is transparent to a YAG laser,there is usually a sufficient amount of sp2 bonded carbon (as found ingraphite) to allow cutting to take place. If not, then a line may bedrawn on the diamond film using a carbon-based ink. The line should besufficient to permit cutting to start, and once started, cutting willproceed slowly.

After an appropriately-sized piece of diamond has been cut from adiamond film, it can be attached to a desired object in order to serveas a surface. For example, the diamond may be attached to a substrate bywelding, diffusion bonding, adhesion bonding, mechanical fixation orhigh pressure and high temperature bonding in a press.

Although CVD and PVD diamond on a substrate do not exhibit a gradienttransition zone that is found in sintered polycrystalline diamondcompacts, CVD and PVD process can be conducted in order to incorporatemetal into the diamond table. As mentioned elsewhere herein,incorporation of metal into the diamond table enhances adhesion of thediamond table to its substrate and can strengthen the polycrystallinediamond compact. Incorporation of diamond into the diamond table can beused to achieve a diamond table with a coefficient of thermal expansionand compressibility different from that of pure diamond, andconsequently increasing fracture toughness of the diamond table ascompared to pure diamond. Diamond has a low coefficient of thermalexpansion and a low compressibility compared to metals. Therefore thepresence of metal with diamond in the diamond table achieves a higherand more metal-like coefficient of thermal expansion and the averagecompressibility for the diamond table than for pure diamond.Consequently, residual stresses at the interface of the diamond tableand the substrate are reduced, and delamination of the diamond tablefrom the substrate is less likely.

A pure diamond crystal also has low fracture toughness. Therefore, inpure diamond, when a small crack is formed, the entire diamond componentfails catastrophically. In comparison, metals have a high fracturetoughness and can accommodate large cracks without catastrophic failure.Incorporation of metal into the diamond table achieves a greaterfracture toughness than pure diamond. In a diamond table havinginterstitial spaces and metal within those interstitial spaces, if acrack forms in the diamond and propagates to an interstitial spacecontaining metal, the crack will terminate at the metal and catastrophicfailure will be avoided. Because of this characteristic, a diamond tablewith metal in its interstitial spaces is able to sustain much higherforces and workloads without catastrophic failure compared to purediamond.

Diamond-diamond bonding tends to decrease as metal content in thediamond table increases. CVD and PVD processes can be conducted so thata transition zone is established. However, the surface may beessentially pure PCD for low wear properties.

Generally CVD and PVD diamond is formed without large interstitialspaces filled with metal. Consequently, most PVD and CVD diamond is morebrittle or has a lower fracture toughness than sintered PDCs. CVD andPVD diamond may also exhibit the maximum residual stresses possiblebetween the diamond table and the substrate. It is possible, however, toform CVD and PVD diamond film that has metal incorporated into it witheither a uniform or a functionally gradient composition.

One method for incorporating metal into a CVD or PVD diamond film is touse two different source materials in order to simultaneously depositthe two materials on a substrate in a CVD of PVD diamond productionprocess. This method may be used regardless of whether diamond is beingproduced by CVD, PVD or a combination of the two.

Another method for incorporating metal into a CVD diamond film chemicalvapor infiltration. This process would first create a porous layer ofmaterial, and then fill the pores by chemical vapor infiltration. Theporous layer thickness should be approximately equal to the desiredthickness for either the uniform or gradient layer. The size anddistribution of the pores can be used to control ultimate composition ofthe layer. Deposition in vapor infiltration occurs first at theinterface between the porous layer and the substrate. As depositioncontinues, the interface along which the material is deposited movesoutward from the substrate to fill pores in the porous layer. As thegrowth interface moves outward, the deposition temperature along theinterface is maintained by moving the sample relative to a heater or bymoving the heater relative to the growth interface. It is imperativethat the porous region between the outside of the sample and the growthinterface be maintained at a temperature that does not promotedeposition of material (either the pore-filling material or undesiredreaction products). Deposition in this region would close the poresprematurely and prevent infiltration and deposition of the desiredmaterial in inner pores. The result would be a substrate with openporosity and poor physical properties.

Laser Deposition of Diamond

Another alternative manufacturing process that may be used to producesurfaces and components involves use of energy beams, such as laserenergy, to vaporize constituents in a substrate and redeposit thoseconstituents on the substrate in a new form, such as in the form of adiamond coating. As an example, a metal, polymeric or other substratemay be obtained or produced containing carbon, carbides or other desiredconstituent elements. Appropriate energy, such as laser energy, may bedirected at the substrate to cause constituent elements to move fromwithin the substrate to the surface of the substrate adjacent the areaof application of energy to the substrate. Continued application ofenergy to the concentrated constituent elements on the surface of thesubstrate can be used to cause vaporization of some of those constituentelements. The vaporized constituents may then be reacted with anotherelement to change the properties and structure of the vaporizedconstituent elements.

Next, the vaporized and reacted constituent elements (which may bediamond) may be diffused into the surface of the substrate. A separatefabricated coating may be produced on the surface of the substratehaving the same or a different chemical composition than that of thevaporized and reacted constituent elements. Alternatively, some of thechanged constituent elements that were diffused into the substrate maybe vaporized and reacted again and deposited as a coating on thesubstrate. By this process and variations of it, appropriate coatingssuch as diamond, cubic boron nitride, diamond like carbon, B₄C, SiC,TiC, TiN, TiB, cCN, Cr₃C₂, and Si₃N₄ may be formed on a substrate.

In other manufacturing environments, high temperature laser application,electroplating, sputtering, energetic laser excited plasma deposition orother methods may be used to place a volume of diamond, diamond-likematerial, a hard material or a superhard material in a location thatwill serve as a surface.

In light of the disclosure herein, those of ordinary skill in the artwill comprehend the apparatuses, materials and process conditionsnecessary for the formation and use of high quality diamond on asubstrate using any of the manufacturing methods described herein inorder to create a diamond surface.

Material Property Considerations

In areas outside of modular bearing inserts and joints, in particular inthe field of rock drilling cutters, polycrystalline diamond compactshave been used for some time. Historically those cutters have beencylindrical in shape with a planar diamond table at one end. The diamondsurface of a cutter is much smaller than the surface needed in mostmodular bearing inserts and joints s. Thus, polycrystalline diamondcutter geometry and manufacturing methods are not directly applicable tomodular bearing inserts and joints.

There is a particular problem posed by the manufacture of a non-planardiamond surface. The non-planar component design requires that pressuresbe applied radially in making the part. During the high pressuresintering process, described in detail below, all displacements must bealong a radian emanating from the center of the sphere that will beproduced to achieve the non-planar geometry. To achieve this in hightemperature/high pressure pressing, an isostatic pressure field must becreated. During the manufacture of such non-planar parts, if there isany deviatoric stress component, it will result in distortion of thepart and may render the manufactured part useless.

Special considerations that must be taken into account in makingnon-planar polycrystalline diamond compacts are discussed below.

Modulus

Most polycrystalline diamond compacts include both a diamond table and asubstrate. The material properties of the diamond and the substrate maybe compatible, but the high pressure and high temperature sinteringprocess in the formation of a polycrystalline diamond compact may resultin a component with excessively high residual stresses. For example, fora polycrystalline diamond compact using tungsten carbide as thesubstrate, the sintered diamond has a Young's modulus of approximately120 million p.s.i., and cobalt cemented tungsten carbide has a modulusof approximately 90 million p.s.i. Modulus refers to the slope of thecurve of the stress plotted against the stress for a material. Modulusindicates the stiffness of the material. Bulk modulus refers to theratio of isostatic strain to isostatic stress, or the unit volumereduction of a material versus the applied pressure or stress.

Because diamond and most substrate materials have such a high modulus, avery small stress or displacement of the polycrystalline diamond compactcan induce very large stresses. If the stresses exceed the yieldstrength of either the diamond or the substrate, the component willfail. The strongest polycrystalline diamond compact is not necessarilystress free. In a polycrystalline diamond compact with optimaldistribution of residual stress, more energy is required to induce afracture than in a stress free component. Thus, the difference inmodulus between the substrate and the diamond must be noted and used todesign a component that will have the best strength for its applicationwith sufficient abrasion resistance and fracture toughness.

Coefficient of Thermal Expansion (“CTE”)

The extent to which diamond and its substrate differ in how they deformrelative to changes in temperature also affects their mechanicalcompatibility. Coefficient of thermal expansion (“CTE”) is a measure ofthe unit change of a dimension with unit change in temperature or thepropensity of a material to expand under heat or to contract whencooled. As a material experiences a phase change, calculations based onCTE in the initial phase will not be applicable. It is notable that whencompacts of materials with different CTEs and moduluses are used, theywill stress differently at the same stress.

PCD has a CTE on the order of 2-4 micro inches per inch (10⁻⁶ inches) ofmaterial per degree (μin/in° C.). In contrast, carbide has a CTE on theorder of 6-8 μin/in° C. Although these values appear to be closenumerically, the influence of the high modulus creates very highresidual stress fields when a temperature gradient of a few hundreddegrees is imposed upon the combination of substrate and diamond. Thedifference in coefficient of thermal expansion is less of a problem insimple planar PDCs than in the manufacture of non-planar or complexshapes. When a non-planar PDC is manufactured, differences in the CTEbetween the diamond and the substrate can cause high residual stresswith subsequent cracking and failure of the diamond table, the substrateor both at any time during or after high pressure/high temperaturesintering.

Dilatoric and Deviatoric Stresses

The diamond and substrate assembly will experience a reduction of freevolume during the sintering process. The sintering process, described indetail below, involves subjecting the substrate and diamond assembly topressure ordinarily in the range of about 40 to about 68 kilobar. Thepressure will cause volume reduction of the substrate. Some geometricaldistortion of the diamond and/or the substrate may also occur. Thestress that causes geometrical distortion is called deviatoric stress,and the stress that causes a change in volume is called dilatoricstress. In an isostatic system, the deviatoric stresses sum to zero andonly the dilatoric stress component remains. Failure to consider all ofthese stress factors in designing and sintering a polycrystallinediamond component with complex geometry (such as concave and convexnon-planar polycrystalline diamond compacts) will likely result infailure of the process.

Free Volume Reduction of Diamond Feedstock

As a consequence of the physical nature of the feedstock diamond, largeamounts of free volume are present unless special preparation of thefeedstock is undertaken prior to sintering. It is necessary to eliminateas much of the free volume in the diamond as possible, and if the freevolume present in the diamond feedstock is too great, then sintering maynot occur. It is also possible to eliminate the free volume duringsintering if a press with sufficient ram displacement is employed. It isimportant to maintain a desired uniform geometry of the diamond andsubstrate during any process that reduces free volume in the feedstock,or a distorted or faulty component may result.

Selection of Solvent-Catalyst Metal

Formation of synthetic diamond in a high temperature and high pressurepress without the use of a solvent-catalyst metal is not a viable methodat this time, although it may become viable in the future. Asolvent-catalyst metal is required to achieve desired crystal formationin synthetic diamond. The solvent-catalyst metal first solvates carbonpreferentially from the sharp contact points of the diamond feedstockcrystals. It then recrystallizes the carbon as diamond in theinterstices of the diamond matrix with diamond-diamond bondingsufficient to achieve a solid with 95 to 97% of theoretical density withsolvent metal 5-3% by volume. That solid distributed over the substratesurface is referred to herein as a polycrystalline diamond table. Thesolvent-catalyst metal also enhances the formation of chemical bondswith substrate atoms.

A method for adding the solvent-catalyst metal to diamond feedstock isby causing it to sweep from the substrate that contains solvent-catalystmetal during high pressure and high temperature sintering. Powderedsolvent-catalyst metal may also be added to the diamond feedstock beforesintering, particularly if thicker diamond tables are desired. Anattritor method may also be used to add the solvent-catalyst metal todiamond feedstock before sintering. If too much or too littlesolvent-catalyst metal is used, then the resulting part may lack thedesired mechanical properties, so it is important to select an amount ofsolvent-catalyst metal and a method for adding it to diamond feedstockthat is appropriate for the particular part to be manufactured.

Diamond Feedstock Particle Size and Distribution

The durability of the finished diamond product is integrally linked tothe size of the feedstock diamond and also to the particle distribution.Selection of the proper size(s) of diamond feedstock and particledistribution depends upon the service requirement of the specimen andalso its working environment. The durability of polycrystalline diamondis enhanced if smaller diamond feedstock crystals are used and a highlydiamond-diamond bonded diamond table is achieved.

Although polycrystalline diamond may be made from single modal diamondfeedstock, use of multi-modal feedstock increases both impact strengthand wear resistance. The use of a combination of large crystal sizes andsmall crystal sizes of diamond feedstock together provides a part withhigh impact strength and wear resistance, in part because theinterstitial spaces between the large diamond crystals may be filledwith small diamond crystals. During sintering, the small crystals willsolvate and reprecipitate in a manner that binds all of the diamondcrystals into a strong and tightly bonded compact.

Diamond Feedstock Loading Methodology

Contamination of the diamond feedstock before or during loading willcause failure of the sintering process. Great care must be taken toensure the cleanliness of diamond feedstock and any addedsolvent-catalyst metal or binder before sintering.

In order to prepare for sintering, clean diamond feedstock, substrate,and container components are prepared for loading. The diamond feedstockand the substrate are placed into a refractory metal container called a“can” which will seal its contents from outside contamination. Thediamond feedstock and the substrate will remain in the can whileundergoing high pressure and high temperature sintering in order to forma polycrystalline diamond compact. The can may be sealed by electronbeam welding at high temperature and in a vacuum.

Enough diamond aggregate (powder or grit) is loaded to account forlinear shrinkage during high pressure and high temperature sintering.The method used for loading diamond feedstock into a can for sinteringaffects the general shape and tolerances of the final part. Inparticular, the packing density of the feedstock diamond throughout thecan should be as uniform as possible in order to produce a good qualitysintered polycrystalline diamond compact structure. In loading, bridgingof diamond can be avoided by staged addition and packing.

The degree of uniformity in the density of the feedstock material afterloading will affect geometry of the PDC. Loading of the feedstockdiamond in a dry form versus loading diamond combined with a binder andthe subsequent process applied for the removal of the binder will alsoaffect the characteristics of the finished PDC. In order to properlypre-compact diamond for sintering, the pre-compaction pressures shouldbe applied under isostatic conditions.

Selection of Substrate Material

The unique material properties of diamond and its relative differencesin modulus and CTE compared to most potential substrate materialsdiamond make selection of an appropriate polycrystalline diamondsubstrate a formidable task. A great disparity in material propertiesbetween the diamond and the substrate creates challenges for successfulmanufacture of a PDC with the requisite strength and durability. Evenvery hard substrates appear to be soft compared to PCD. The substrateand the diamond must be able to withstand not only the pressure andtemperature of sintering, but must be able to return to room temperatureand atmospheric pressure without delaminating, cracking or otherwisefailing.

Selection of substrate material also requires consideration of theintended application for the part, impact resistance and strengthsrequired, and the amount of solvent-catalyst metal that will beincorporated into the diamond table during sintering. Substratematerials must be selected with material properties that are compatiblewith those of the diamond table to be formed.

Substrate Geometry

Further, it is important to consider whether to use a substrate that hasa smooth surface or a surface with topographical features. Substratesurfaces may be formed with a variety of topographical features so thatthe diamond table is fixed to the substrate with both a chemical bondand a mechanical grip. Use of topographical features on the substrateprovides a greater surface area for chemical bonds and with themechanical grip provided by the topographical features, can result in astronger and more durable component.

Example Materials and Manufacturing Steps

The inventors have discovered and determined materials and manufacturingprocesses for constructing PDCs for use in a modular bearing inserts andjoints. It is also possible to manufacture the invented surfaces bymethods and using materials other than those listed below.

The steps described below, such as selection of substrate material andgeometry, selection of diamond feedstock, loading and sintering methods,will affect each other, so although they are listed as separate stepsthat must be taken to manufacture a PDC or a compact of polycrystallinecubic boron nitride, no step is completely independent of the others,and all steps must be standardized to ensure success of themanufacturing process.

Select Substrate Material and/or Solvent-Catalyst Metal

In order to manufacture any polycrystalline component, an appropriatesubstrate should be selected (unless the component is to be freestanding without a substrate).

TABLE 2 SOME SUBSTRATES FOR PROSTHETIC JOINT APPLICATIONS SUBSTRATEALLOY NAME REMARKS Titanium Ti6/4 (TiAlVa) A thin tantalum barrier ASTMF-1313 (TiNbZr) may be placed on the ASTM F-620 titanium substratebefore ASTM F-1580 loading diamond TiMbHf feedstock. Nitinol (TiNi +other) Cobalt chrome ASTM F-799 Contains cobalt, chromium andmolybdenum. Wrought product Cobalt chrome ASTM F-90 Contains cobalt,chromium, tungsten and nickel. Cobalt chrome ASTM F-75 Contains cobalt,chromium and molybdenum. Cast product. Cobalt chrome ASTM F-562 Containscobalt, chromium, molybdenum and nickel. Cobalt chrome ASTM F-563Contains cobalt, chromium, molybdenum, tungsten, iron and nickel.Tantalum ASTM F-560 (unalloyed) Refractory metal. Platinum variousNiobium ASTM F-67 (unalloyed) Refractory metal. Maganese Various Mayinclude Cr, Ni, Mg, molybdenum. Cobalt cemented WC Commonly used intungsten carbide synthetic diamond production Cobalt chrome CoCrcemented WC cemented tungsten carbide Cobalt chrome CoCr cemented CrCcemented chrome carbide Cobalt chrome CoCr cemented SiC cemented siliconcarbide Fused silicon SiC carbide Cobalt chrome CoCrMo A thin tungstenor molybdenum tungsten/cobalt layer may be placed on the substratebefore loading diamond feedstock. Stainless steel Various

The CoCr used as a substrate or solvent-catalyst metal may be CoCrMo orCoCrW or another suitable CoCr. Alternatively, an Fe-based alloy, aNi-based alloy (such as Co-Cr-W-Ni) or another alloy may be used. Co andNi alloys tend to provide a corrosion-resistant component. The precedingsubstrates and solvent-catalyst metals are examples only. In addition tothese substrates, other materials may be appropriate for use assubstrates for construction of modular bearing inserts and joints andother surfaces.

When titanium is used as the substrate, it is possible to place a thintantalum barrier layer on the titanium substrate. The tantalum barrierprevents mixing of the titanium alloys with cobalt alloys used in thediamond feedstock. If the titanium alloys and the cobalt alloys mix, itis possible that a detrimentally low melting point eutecticinter-metallic compound will be formed during the high pressure and hightemperature sintering process. The tantalum barrier bonds to both thetitanium and cobalt alloys, and to the PCD that contains cobaltsolvent-catalyst metals. Thus, a PDC made using a titanium substratewith a tantalum barrier layer and diamond feedstock that has cobaltsolvent-catalyst metals can be very strong and well formed.Alternatively, the titanium substrate may be provided with an alpha caseoxide coating (an oxidation layer) forming a barrier that preventsformation of a eutectic metal.

If a cobalt chrome molybdenum substrate is used, a thin tungsten layeror a thin tungsten and cobalt layer can be placed on the substratebefore loading of the diamond feedstock in order to control formation ofchrome carbide (CrC) during sintering.

In addition to those listed, other appropriate substrates may be usedfor forming PDC surfaces. Further, it is possible within the scope ofthe claims to form a diamond surface for use without a substrate. It isalso possible to form a surface from any of the superhard materials andother materials listed herein, in which case a substrate may not beneeded. Additionally, if it is desired to use a type of diamond orcarbon other than PCD, substrate selection may differ. For example, if adiamond surface is to be created by use of chemical vapor deposition orphysical vapor deposition, then use of a substrate appropriate for thosemanufacturing environments and for the compositions used will benecessary.

Determination of Substrate Geometry

A substrate geometry appropriate for the compact to be manufactured andappropriate for the materials being used should be selected. In order tomanufacture a concave non-planar acetabular cup, a convex non-planarfemoral head, or a non-planar surface, it is necessary to select asubstrate geometry that will facilitate the manufacture of those parts.In order to ensure proper diamond formation and avoid compactdistortion, forces acting on the diamond and the substrate duringsintering must be strictly radial. Therefore the substrate geometry atthe contact surface with diamond feedstock for manufacturing anacetabular cup, a femoral head, or any other non-planar component isgenerally non-planar.

As mentioned previously, there is a great disparity in the materialcharacteristics of synthetic diamond and most available substratematerials. In particular, modulus and CTE are of concern. But whenapplied in combination with each other, some substrates can form astable and strong PDC. The table below lists physical properties of somesubstrate materials.

TABLE 3A MATERIAL PROPERTIES OF SOME SUBSTRATES SUBSTRATE MATERIALMODULUS CTE Ti 6/4 16.5 million psi 5.4 CoCrMo 35.5 million psi 16.9CoCrW 35.3 million psi 16.3

Use of either titanium or cobalt chrome substrates alone for themanufacture of non-planar PDCs may result in cracking of the diamondtable or separation of the substrate from the diamond table. Inparticular, it appears that the dominant property of titanium duringhigh pressure and high temperature sintering is compressibility whilethe dominant property of cobalt chrome during sintering is CTE. In someembodiments, a substrate of two or more layers may be used to achievedimensional stability during and after manufacturing.

In various embodiments, a single layer substrate may be utilized. Inother embodiments, a two-layer substrate may be utilized, as discussed.Depending on the properties of the components being used, however, itmay be desired to utilize a substrate that includes three, four or morelayers. Such multi-layer substrates are intended to be comprehendedwithin the scope of the claims.

Substrate Surface Topography

Depending on the application, it may be advantageous to includesubstrate surface topographical features on a substrate that is to beformed into a PDC. Regardless whether a one-piece, a two-piece of amulti-piece substrate is used, it may be desirable to modify the surfaceof the substrate or provide topographical features on the substrate toincrease the total surface area of diamond to enhance substrate todiamond contact and to provide a mechanical grip of the diamond table.

The placement of topographical features on a substrate serves to modifythe substrate surface geometry or contours from what the substratesurface geometry or contours would be if formed as a simple planar ornon-planar figure. Substrate surface topographical features may includeone or more different types of topographical features that result inprotruding, indented or contoured features that serve to increasesurface, mechanically interlock the diamond table to the substrate,prevent crack formation, or prevent crack propagation.

Substrate surface topographical features or substrate surfacemodifications serve a variety of useful functions. Use of substratetopographical features increases total substrate surface area of contactbetween the substrate and the diamond table. This increased surface areaof contact between diamond table and substrate results in a greatertotal number of chemical bonds between diamond table and substrate thanif the substrate surface topographical features were absent, thusachieving a stronger PDC.

Substrate surface topographical features also serve to create amechanical interlock between the substrate and the diamond table. Themechanical interlock is achieved by the nature of the substratetopographical features and also enhances strength of the PDC.

Substrate surface topographical features may also be used to distributethe residual stress field of the PDC over a larger surface area and overa larger volume of diamond and substrate material. This greaterdistribution can be used to keep stresses below the threshold for crackinitiation and/or crack propagation at the diamond table/substrateinterface, within the diamond itself and within the substrate itself.

Substrate surface topographical features increase the depth of thegradient interface or transition zone between diamond table andsubstrate, in order to distribute the residual stress field through alonger segment of the composite compact structure and to achieve astronger part.

Substrate surface modifications can be used to created a sintered PDCthat has residual stresses that fortify the strength of the diamondlayer and yield a more robust PDC with greater resistance to breakagethan if no surface topographical features were used. This is because inorder to break the diamond layer, it is necessary to first overcome theresidual stresses in the part and then overcome the strength of thediamond table.

Substrate surface topographical features redistribute forces received bythe diamond table. Substrate surface topographical features cause aforce transmitted through the diamond layer to be retransmitted fromsingle force vector along multiple force vectors. This redistribution offorces traveling to the substrate avoids conditions that would deformthe substrate material at a more rapid rate than the diamond table, assuch differences in deformation can cause cracking and failure of thediamond table.

Substrate surface topographical features may be used to mitigate theintensity of the stress field between the diamond and the substrate inorder to achieve a stronger part.

Substrate surface topographical features may be used to distribute theresidual stress field throughout the PDC structure in order to reducethe stress per unit volume of structure.

Substrate surface topographical features may be used to mechanicallyinterlock the diamond table to the substrate by causing the substrate tocompress over an edge of the diamond table during manufacturing.Dovetailed, non-planar and lentate modifications act to provide forcevectors that tend to compress and enhance the interface of diamond tableand substrate during cooling as the substrate dilitates radially.

Substrate surface topographical features may also be used to achieve amanufacturable form. As mentioned herein, differences in coefficient ofthermal expansion and modulus between diamond and the chosen substratemay result in failure of the PDC during manufacturing. For certainparts, the stronger interface between substrate and diamond table thatmay be achieved when substrate topographical features are used canachieve a polycrystalline diamond compact that can be successfullymanufactured. But if a similar part of the same dimensions is to be madeusing a substrate with a simple substrate surface rather thanspecialized substrate surface topographical features, the diamond tablemay crack or separate from the substrate due to differences incoefficient of thermal expansion or modulus of the diamond and thesubstrate.

Examples of useful substrate surface topographical features includewaves, grooves, ridges, other longitudinal surface features (any ofwhich may be arranged longitudinally, lattitudinally, crossing eachother at a desired angle, in random patterns, and in geometricpatterns), three dimensional textures, non-planar segment depressions,non-planar segment protrusions, triangular depressions, triangularprotrusions, arcuate depressions, arcuate protrusions, partiallynon-planar depressions, partially non-planar protrusions, cylindricaldepressions, cylindrical protrusions, rectangular depressions,rectangular protrusions, depressions of n-sided polygonal shapes where nis an integer, protrusions of n-sided polygonal shapes, a waffle patternof ridges, a waffle iron pattern of protruding structures, dimples,nipples, protrusions, ribs, fenestrations, grooves, troughs or ridgesthat have a cross-sectional shape that is rounded, triangular, arcuate,square, polygonal, curved, or otherwise, or other shapes. Machining,pressing, extrusion, punching, injection molding and other manufacturingtechniques for creating such forms may be used to achieve desiredsubstrate topography. Illustration of example substrate topographicalfeatures is found in U.S. Pat. No. 6,709,463 which is herebyincorporated by reference in its entirety.

Although many substrate topographies have been depicted in convexnon-planar substrates, those surface topographies may be applied toconvex non-planar substrate surfaces, other non-planar substratesurfaces, and flat substrate surfaces. Substrate surface topographieswhich are variations or modifications of those shown, and othersubstrate topographies which increase component strength or durabilitymay also be used.

Diamond Feedstock Selection

It is anticipated that typically the diamond particles used will be inthe range of less than 1 micron to more than 100 microns. In someembodiments, however, diamond particles as small as 1 nanometer may beused. Smaller diamond particles are preferred for smoother surfaces.Commonly, diamond particle sizes will be in the range of 0.5 to 2.0microns or 0.1 to 10 microns.

An example diamond feedstock is shown in the table below.

TABLE 3B EXAMPLE BIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT   4 to 8micron diamond about 90% 0.5 to 1.0 micron diamond about 9% Titaniumcarbonitride powder about 1%

This formulation mixes some smaller and some larger diamond crystals sothat during sintering, the small crystals may dissolve and thenrecrystallize in order to form a lattice structure with the largerdiamond crystals. Titanium carbonitride powder may optionally beincluded in the diamond feedstock to prevent excessive diamond graingrowth during sintering in order to produce a finished product that hassmaller diamond crystals.

Another diamond feedstock example is provided in the table below.

TABLE 4 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size ×diamond crystals about 90% Size 0.1 × diamond crystals about 9% Size0.01 × diamond crystals about 1%

The trimodal diamond feedstock described above can be used with anysuitable diamond feedstock having a first size or diameter “x”, a secondsize 0.1x and a third size 0.01x. This ratio of diamond crystals allowspacking of the feedstock to about 89% theoretical density, closing mostinterstitial spaces and providing the densest diamond table in thefinished polycrystalline diamond compact.

Another diamond feedstock example is provided in the table below.

TABLE 5 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size ×diamond crystals about 88-92% Size 0.1 × diamond crystals about 8-12%Size 0.01 × diamond crystals about 0.8-1.2%

Another diamond feedstock example is provided in the table below.

TABLE 6 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size ×diamond crystals about 85-95% Size 0.1 × diamond crystals about 5-15%Size 0.01 × diamond crystals about 0.5-1.5%

Another diamond feedstock example is provided in the table below.

TABLE 7 EXAMPLE TRIMODAL DIAMOND FEEDSTOCK MATERIAL AMOUNT Size ×diamond crystals about 80-90% Size 0.1 × diamond crystals about 10-20%Size 0.01 × diamond crystals about 0-2%

In some embodiments, the diamond feedstock used will be diamond powderhaving a greatest dimension of about 100 nanometers or less. In someembodiments some solvent-catalyst metal is included with the diamondfeedstock to aid in the sintering process, although in many applicationsthere will be a significant solvent-catalyst metal sweep from thesubstrate during sintering as well.

Solvent Metal Selection

It has already been mentioned that solvent metal will sweep from thesubstrate through the diamond feedstock during sintering to solvate somediamond crystals so that they may later recrystallize and form adiamond-diamond bonded lattice network that characterizes PCD. In theevent of making a freestanding compact of PCD without a substrate,solvent metal may be mixed with diamond crystals before sintering toachieve the same result. Even if a substrate is being used, It ispossible to include some solvent-catalyst metal in the diamond feedstockwhen desired to supplement the sweep of solvent-catalyst metal from thesubstrate.

Traditionally, cobalt, nickel and iron have been used as solvent metalsfor making PCD. Platinum and other materials could also be used for abinder.

CoCr may be used as a solvent-catalyst metal for sintering PCD toachieve a more wear resistant PDC. Infiltrating diamond particles withCobalt (Co) metal produces standard PDC. As the cobalt infiltrates thediamond, carbon is dissolved (mainly from the smaller diamond grains)and reprecipitates onto the larger diamond grains causing the grains togrow together. This is known as liquid phase sintering. The remainingpore spaces between the diamond grains are filled with cobalt metal.

In one example, the alloy Cobalt Chrome (CoCr) may be used as thesolvent metal which acts similarly to Co metal. However, it differs inthat the CoCr reacts with some of the dissolved carbon resulting in theprecipitation of CoCr carbides. These carbides, like most carbides, areharder (abrasion resistant) than cobalt metal and results in a more wearor abrasion resistant PDC.

Other metals can be added to Co to form metal carbides as precipitateswithin the pore spaces between the diamond grains. These metals includethe following, but not limited to, Ti, W, Mo, V, Ta, Nb, Zr, Si, andcombinations thereof.

It is important not just to add the solvent metal to diamond feedstock,but also to include solvent metal in an appropriate proportion and tomix it evenly with the feedstock. The use of about 86% diamond feedstockand 15% solvent metal by mass (weight) has provided good result, otherratios of diamond feedstock to solvent metal may include 5:95, 10:90,20:80, 30:70, 40:60, 50:50, 60:40, 65:35, 75:25, 80:20, 90:10, 95:5,97:3, 98:2, 99:1, 99.5:0.5, 99.7:0.3, 99.8:0.2, 99.9:0.1 and others.

In order to mix the diamond feedstock with solvent-catalyst metal, firstthe amounts of feedstock and solvent metal to be mixed may be placedtogether in a mixing bowl, such as a mixing bowl made of the desiredsolvent-catalyst metal. Then the combination of feedstock and solventmetal may be mixed at an appropriate speed (such as 200 rpm) with drymethanol and attritor balls for an appropriate time period, such as 30minutes. The attritor balls, the mixing fixture and the mixing bowl maybe made from the solvent-catalyst metal. The methanol may then bedecanted and the diamond feedstock separated from the attritor balls.The feedstock may then be dried and cleaned by firing in a molecularhydrogen furnace at about 1000 degrees Celsius for about 1 hour. Thefeedstock is then ready for loading and sintering. Alternatively, it maybe stored in conditions that will preserve its cleanliness. Appropriatefurnaces that may be used for firing also include hydrogen plasmafurnaces and vacuum furnaces.

Loading Diamond Feedstock

Referring to FIG. 1E, an apparatus for carrying out a loading techniqueis depicted. The apparatus includes a spinning rod 151 with alongitudinal axis 152, the spinning rod being capable of spinning aboutits longitudinal axis. The spinning rod 151 has an end 153 matched tothe size and shape of the part to be manufactured. For example, if thepart to be manufactured is non-planar, the spinning rod end 153 may benon-planar.

A compression ring 154 is provided with a bore 155 through which thespinning rod 151 may project. A die 156 or can is provided with a cavity157 also matched to the size and shape of the part to be made.

In order to load diamond feedstock, the spinning rod is placed into adrill chuck and the spinning rod is aligned with the center point of thedie. The depth to which the spinning rod stops in relation to the cavityof the die is controlled with a set screw and monitored with a dialindicator.

The die is charged with a known amount of diamond feedstock material.The spinning rod is then spun about its longitudinal axis and loweredinto the die cavity to a predetermined depth. The spinning rod contactsand rearranges the diamond feedstock during this operation. Then thespinning of the spinning rod is stopped and the spinning rod is lockedin place.

The compression ring is then lowered around the outside of the spinningrod to a point where the compression ring contacts diamond feedstock inthe cavity of the die. The part of the compression ring that contactsthe diamond is annular. The compression ring is tamped up and down tocompact the diamond. This type of compaction is used to distributediamond material throughout the cavity to the same density and may bedone in stages to prevent bridging. Packing the diamond with thecompaction ring causes the density of the diamond around the equator ofthe sample to be very uniform and the same as that of the polar regionin the cavity. In this configuration, the diamond sinters in a trulynon-planar fashion and the resulting part maintains its sphericity toclose tolerances.

Controlling Large Volumes of Powder Feedstocks, Such As Diamond

The following information provides further instruction on control andpre-processing of diamond feedstock before sintering. PDC andPolycrystalline Cubic Boron Nitride (PCBN) powders reduce in volumeduring the sintering process. The amount of shrinkage experienced isdependent on a number of factors such as:

-   -   1. The amount of metal mixed with the diamond.    -   2. The loading density of the powders.    -   3. The bulk density of diamond metal mix.    -   4. The volume of powder loaded.    -   5. Particle size distribution (PSD) of the powders.

In most PDC and PCBN sintering applications, the volume of powder usedis small enough that shrinkage is easily managed, as shown in FIG. 3A-1.FIG. 3A-1 illustrates a can 3A-54 in which can halves 3A-53 contain asubstrate 3A-52 and a diamond table 3A-51. However, when sintering largevolumes of diamond powders in spherical configurations, shrinkage isgreat enough to cause buckling of the containment cans 3A-66 as shown inFIG. 3A-2 and the cross section of FIG. 3A-3. The diamond has sintered3A-75 but the can has buckles 3A-77 and wrinkles 3A-78, resulting in anon-uniform and damaged part. The following method is an improvedloading, pre-compression, densification, and refractory can sealingmethod for spherical and non-planar parts loaded with large volumes ofdiamond and/or metal powders. The processing steps are described below.

Referring to FIG. 3A-4 and its cross section at FIG. 3A-5, PDC or PCBNpowders 3A-911 are loaded against a substrate 3A-99 and into arefractory metal containment can assembly 3A-913 having can half skins3A-910 and a seal 3A-912. Extra powder may be loaded normal to the seamin the can to accommodate shrinkage.

Referring to FIG. 3A-6, a can assembly 3A-913 is placed into acompaction fixture 3A-1014, which may be a cylindrical holder or slide3A-1015 with two hemispherical punches 3A-1016 and 3A-1017. The fixtureis designed to support the containment cans and allow the can half skins3A-910 to slip at the seam during the pressing operation.

Referring to FIG. 3A-7-1, the relationship of the can half skins 3A-910with the junction 3A-912 and the punch 3A-1016 is seen.

Referring to FIG. 3A-7, illustrates a compaction fixture 3A-1014 with acan 3A-913 placed into a press 3A-1218 and the upper 3A-1016 and lower3A-1017 punches compress the can assembly 3A-913. The containment canhalves 3A-910 slip past each other preventing buckling while thepowdered feedstock is compressed.

Referring to FIG. 3A-8, the upper punch 3A-24 and upper press fitting3A-25 are retracted and a crimping die 3A-20 is attached to the cylinderof the compaction fixture 3A-21. The can assembly 3A-913 rests againstthe lower punch 3A-22 that is attached to the lower press fitting 3A-23.

Referring to FIGS. 3A-9 and 3A-9-1, the lower punch 3A-22 is raisedtoward the upper punch 3A-24 driving excess can material 3A-27 into thehemispherical portion of the crimping die 3A-19 folding the excessaround the upper can 3A-26.

Referring to FIG. 3A-10, the lower punch is raised expelling the canassembly 3A-13 from the cylinder 3A-28 of the compaction fixture 3A-21.

Referring to FIG. 3A-11, the can assembly 3A-913 emerges from pressingoperation spherical with high loading density. The part may then besintered in a cubic or other press without buckling or breaking thecontainment cans as the can half skins 3A-910 are overlapped.

Binding Diamond Feedstock Generally

Another method that may be employed to maintain a uniform density of thefeedstock diamond is the use of a binder. A binder is added to thecorrect volume of feedstock diamond, and then the combination is pressedinto a can. Some binders that may be used include polyvinyl butyryl,polymethyl methacrylate, polyvinyl formol, polyvinyl chloride acetate,polyethylene, ethyl cellulose, methylabietate, paraffin wax,polypropylene carbonate and polyethyl methacrylate.

In one embodiment, the process of binding diamond feedstock includesfour steps. First, a binder solution is prepared. A binder solution maybe prepared by adding about 5 to 25% plasticizer to pellets of poly(propylene carbonate), and dissolving this mixture in solvent such as2-butanone to make about a 20% solution by weight.

Plasticizers that may be used include nonaqueous binders generally,glycol, dibutyl phthalate, benzyl butyl phthalate, alkyl benzylphthalate, diethylhexyl phthalate, diisoecyl phthalate, diisononylphthalate, dimethyl phthalate, dipropylene glycol dibenzoate, mixedglycols dibenzoate, 2-ethylhexyl diphenyl dibenzoate, mixed glycolsdibenzoate, 2-ethylhexyl diphenyl phosphate, isodecyl diphenylphosphate, isodecyl diphenl phosphate, tricrestyl phosphate, tributoxyethyl phosphate, dihexyl adipate, triisooctyl trimellitate, dioctylphthalate, epoxidized linseed oil, epoxidized soybean oil, acetyltriethyl citrate, propylene carbonate, various phthalate esters, butylstearate, glycerin, polyalkyl glycol derivatives, diethyl oxalate,paraffin wax and triethylene glycol. Other appropriate plasticizers maybe used as well.

Solvents that may be used include 2-butanone, methylene chloride,chloroform, 1,2-dichloroethne, trichlorethylene, methyl acetate, ethylacetate, vinyl acetate, propylene carbonate, n-propyl acetate,acetonitrile, dimethylformamide, propionitrile, n-mehyl-2-pyrrolidene,glacial acetic acid, dimethyl sulfoxide, acetone, methyl ethyl ketone,cyclohexanone, oxysolve 80a, caprotactone, butyrolactone,tetrahydrofuran, 1,4 dioxane, propylene oxide, cellosolve acetate,2-methoxy ethyl ether, benzene, styrene, xylene, ethanol, methanol,toluene, cyclohexane, chlorinated hydrocarbons, esters, ketones, ethers,ethyl benzene and various hydrocarbons. Other appropriate solvents maybe used as well.

Second, diamond is mixed with the binder solution. Diamond may be addedto the binder solution to achieve about a 2-25% binder solution (thepercentage is calculated without regard to the 2-butanone).

Third, the mixture of diamond and binder solution is dried. This may beaccomplished by placing the diamond and binder solution mixture in avacuum oven for about 24 hours at about 50 degrees Celsius to drive outall of the solvent 2-butanone.

Fourth, the diamond and binder may be pressed into shape. When thediamond and binder is removed from the oven, it will be in a clump thatmay be broken into pieces that are then pressed into the desired shapewith a compaction press. A pressing spindle of the desired geometry maybe contacted with the bound diamond to form it into a desired shape.When the diamond and binder have been pressed, the spindle is retracted.The final density of diamond and binder after pressing may be at leastabout 2.6 grams per cubic centimeter.

If a volatile binder is used, it should be removed from the shapeddiamond prior to sintering. The shaped diamond is placed into a furnaceand the binding agent is either gasified or pyrolized for a sufficientlength of time such that there is no binder remaining. PDC quality isreduced by foreign contamination of the diamond or substrate, and greatcare must be taken to ensure that contaminants and binder are removedduring the furnace cycle. Ramp up and the time and temperaturecombination are critical for effective pyrolization of the binder. Forthe binder example given above, the debinding process may be used toremove the binder is as follows. (Referring to FIG. 1F while readingthis description may be helpful.)

First, the shaped diamond and binder are heated from ambient temperatureto about 500 degrees Celsius. The temperature may be increased by about2 degrees Celsius per minute until about 500 degrees Celsius is reached.Second, the temperature of the bound and shaped diamond is maintained atabout 500 degrees Celsius for about 2 hours. Third, the temperature ofthe diamond is increased again. The temperature may be increased fromabout 500 degrees Celsius by about 4 degrees per minute until atemperature of about 950 degrees Celsius is reached. Fourth, the diamondis maintained at about 950 degrees Celsius for about 6 hours. Fifth, thediamond is then permitted to return to ambient temperature at atemperature decrease of about 2 degrees per minute.

In some embodiments, it may be desirable to preform bound diamondfeedstock by an appropriate process, such as injection molding. Thediamond feedstock may include diamond crystals of one or more sizes,solvent-catalyst metal, and other ingredients to control diamondrecrystallization and solvent-catalyst metal distribution. Handling thediamond feedstock is not difficult when the desired final curvature ofthe part is flat, convex dome or conical. However, when the desiredfinal curvature of the part has complex contours, such as illustratedherein, providing uniform thickness and accuracy of contours of the PDCis more difficult when using powder diamond feedstock. In such cases itmay be desirable to preform the diamond feedstock before sintering.

If it is desired to preform diamond feedstock prior to loading into acan for sintering, rather than placing powder diamond feedstock into thecan, the steps described herein and variations of them may be followed.First, as already described, a suitable binder is added to the diamondfeedstock. Optionally, powdered solvent-catalyst metal and othercomponents may be added to the feedstock as well. The binder willtypically be a polymer chosen for certain characteristics, such asmelting point, solubility in various solvents, and CTE. One or morepolymers may be included in the binder. The binder may also include anelastomer and/or solvents as desired in order to achieve desiredbinding, fluid flow and injection molding characteristics. The workingvolume of the binder to be added to a feedstock may be equal to orslightly more than the measured volume of empty space in a quantity oflightly compressed powder. Since binders typically consist of materialssuch as organic polymers with relatively high CTEs, the working volumeshould be calculated for the injection molding temperatures expected.The binder and feedstock should be mixed thoroughly to assure uniformityof composition. When heated, the binder and feedstock will havesufficient fluid character to flow in high pressure injection molding.The heated feedstock and binder mixture is then injected under pressureinto molds of desired shape. The molded part then cools in the molduntil set, and the mold can then be opened and the part removed.Depending on the final PDC geometry desired, one or more molded diamondfeedstock components can be created and placed into a can for PDCsintering. Further, use of this method permits diamond feedstock to bemolded into a desired form and then stored for long periods of timeprior to use in the sintering process, thereby simplifying manufacturingand resulting in more efficient production.

As desired, the binder may be removed from the injection molded diamondfeedstock form. A variety of methods are available to achieve this. Forexample, by simple vacuum or hydrogen furnace treatment, the binder maybe removed from the diamond feedstock form. In such a method, the formwould be brought up to a desired temperature in a vacuum or in a verylow pressure hydrogen (reducing) environment. The binder will thenvolatilize with increasing temperature and will be removed from theform. The form may then be removed from the furnace. When hydrogen isused, it helps to maintain extremely clean and chemically activesurfaces on the diamond crystals of the diamond feedstock form.

An alternative method for removing the binder from the form involvesutilizing two or polymer (such as polyethylene) binders with differentmolecular weights. After initial injection molding, the diamondfeedstock form is placed in a solvent bath that removes the lowermolecular weight polymer, leaving the higher molecular weight polymer tomaintain the shape of the diamond feedstock form. Then the diamondfeedstock form is placed in a furnace for vacuum or very low pressurehydrogen treatment for removal of the higher molecular weight polymer.

Partial or complete binder removal from the diamond feedstock form maybe performed prior to assembly of the form in a pressure assembly forPDC sintering. Alternatively, the pressure assembly including thediamond feedstock form may be placed into a furnace for vacuum or verylow pressure hydrogen furnace treatment and binder removal.

Dilute Binder

In some embodiments, dilute binder may be added to PCD, PCBN or ceramicpowders to hold form. This technique may be used to provide an improvedmethod of forming PDC, PCBN, ceramic, or cermet powders into layers ofvarious geometries. A PDC, PCBN, ceramic or cermet powder may be mixedwith a temporary organic binder. This mixture may be mixed and cast orcalendared into a sheet (tape) of the desired thickness. The sheet maybe dried to remove water or organic solvents. The dried tape may be thencut into shapes needed to conform to the geometry of a correspondingsubstrate. The tape/substrate assembly may be then heated in a vacuumfurnace to drive off the binder material. The temperature may then beraised to a level where the ceramic or cermet powder fuses to itselfand/or to the substrate, thereby producing a uniform continuous ceramicor cermet coating bonded to the substrate.

Referring to FIG. 5, a die 55 with a cup/can in it 54 and diamondfeedstock 52 against it are depicted. A punch 53 is used to form thediamond feedstock 52 into a desired shape. Binder liquid 51 is not addedto the powder until after the diamond, PCBN, ceramic or cermet powder 52is in the desired geometry. Dry powder 52 is spin formed using arotating formed punch 53 in a refractory containment can 54 supported ina holding die 55. In another method shown in FIG. 6, feedstock powder 62is added to a mold 66. A punch forms the feedstock to shape. A vibrator67 may be used help the powder 62 take on the shape of the mold 66.After the powder feedstock is in the desired geometry, a dilute solutionof an organic binder with a solvent is allowed to percolate through thepowder granules.

As shown in FIGS. 7 and 8, one powder layer 88 can be loaded, and aftera few minutes, when the binder is cured sufficiently at roomtemperature, another layer 89 can be loaded on top of the first layer88. This method is particularly useful in producing PDC or PCBN withmultiple layers of varying powder particle size and metal content. Theprocess can be repeated to many layers as desired. FIG. 7 shows asection view of a spherical, multi-layered powder load using a firstlayer 88, second layer 89, third layer 810, and final layer 811. Thebinder content should be kept to a minimum to produce good loadingdensity and to limit the amount of gas produced during the binderremoval phase to reduce the tendency of the containment cans 84 beingdisplaced from a build up of internal pressure.

Once all of the powder layers are loaded the binder may be burned-out ina vacuum oven at a vacuum of about 200 Militorrs or less and at the timeand desired temperature profile, such as that shown in FIG. 9. Anacceptable binder is 0.5 to 5% propylene carbonate in methyl ethylkeytone. An example binder burn out cycle that may be used to removebinder is as follows:

Time Temperature (minutes) (degrees Centigrade) 0 21 4 100 8 250 60 250140 800 170 800 290 21Gradients

Diamond feedstock may be selected and loaded in order to createdifferent types of gradients in the diamond table. These include aninterface gradient diamond table, an incremental gradient diamond table,and a continuous gradient diamond table.

If a single type or mix of diamond feedstock is loaded adjacent asubstrate, as discussed elsewhere herein, sweep of solvent-catalystmetal through the diamond will create an interface gradient in thegradient transition zone of the diamond table.

An incremental gradient diamond table may be created by loading diamondfeedstocks of differing characteristics (diamond particle size, diamondparticle distribution, metal content, etc.) in different strata orlayers before sintering. For example, a substrate is selected, and afirst diamond feedstock containing 60% solvent-catalyst metal by weightis loaded in a first strata adjacent the substrate. Then a seconddiamond feedstock containing 40% solvent-catalyst metal by weight isloaded in a second strata adjacent the first strata. Optionally,additional strata of diamond feedstock may be used. For example, a thirdstrata of diamond feedstock containing 20% solvent-catalyst metal byweight may be loaded adjacent the second strata.

A continuous gradient diamond table may be created by loading diamondfeedstock in a manner that one or more of its characteristicscontinuously vary from one depth in the diamond table to another. Forexample, diamond particle size may vary from large near a substrate (tocreate large interstitial spaces in the diamond for solvent-catalystmetal to sweep into) to small near the diamond surface to create a partthat is strongly bonded to the substrate but that has a very lowfriction surface.

The diamond feedstocks of the different strata may be of the same ordifferent diamond particle size and distribution. Solvent-catalyst metalmay be included in the diamond feedstock of the different strata inweight percentages of from about 0% to more than about 80%. In someembodiments, diamond feedstock will be loaded with no solvent-catalystmetal in it, relying on sweep of solvent-catalyst metal from thesubstrate to achieve sintering. Use of a plurality of diamond feedstockstrata, the strata having different diamond particle size anddistribution, different solvent-catalyst metal by weight, or both,allows a diamond table to be made that has different physicalcharacteristics at the interface with the substrate than at the surface.This allows a PDC to be manufactured that has a diamond table veryfirmly bonded to its substrate.

Bisquing Processes to Hold Shapes

If desired, a bisquing process may be used to hold shapes for subsequentprocessing of PDCs, PCBN, and ceramic or cermet products. This involvesan interim processing step in High Temperature High Pressure (HTHP)sintering of PDC, PCBN, ceramic, or cermet powders called “bisquing.”Bisquing may provide the following enhancements to the processing of theabove products:

A. Pre-sintered shapes can be controlled that are at a certain densityand size.

B. Product consistency is improved dramatically.

C. Shapes can be handled easily in the bisque form.

D. In layered constructs, bisquing keeps the different layers fromcontaminating each other.

E. Bisquing different components or layers separately increases theseparation of work elements increasing production efficiency andquality.

F. Bisquing molds are often easer to handle and manage prior to finalassembly than the smaller final product forms.

Bisquing molds or containers can be fabricated from any high temperaturematerial that has a melting point higher than the highest melting pointof any mix component to be bisqued. Bisque mold/container materials thatwork well are Graphite, Quartz, Solid Hexagonal Boron Nitride (HBN), andceramics. Some refractory type metals (high temperature stainlesssteels, Nb, W, Ta, Mo, etc) work well is some applications wherebisquing temperatures are lower and sticking of the bisque powder mix isnot a problem. Molds or containers can be shaped by pressing, forming,or machining, and may be polished at the interface between the bisquematerial and the mold/container itself. Some mold container materialsrequire glazing and/or firing prior to use.

FIG. 10 shows an embodiment 1006 for making a cylinder with a concaverelief or trough using the bisquing process. Pre-mixed powders of PDC,PCBN, ceramic, or cermet materials 1001 that contain enough metal toundergo solid phase sintering are loaded into the bisquing molds orcontainers 1002 and 1004. A release agent may be required between themold/container to ensure that the final bisque form can be removedfollowing furnace firing. Some release agents that may be used are HBN,Graphite, Mica, and Diamond Powder. A bisque mold/container lid with anintegral support form 1005 is placed over the loaded powder material toensure that the material holds form during the sintering process. Thebisque mold/container assembly is then placed in a hydrogen atmospherefurnace, or alternately, in a vacuum furnace which is drawn to a vacuumranging from 200 to 0 Militorrs. The load is then heated within a rangeof 0.6 to 0.8 of the melting temperature of the largest volume mixmetal. A typical furnace cycle is shown in FIG. 12. Once the furnacecycle is completed and the mold/container is cooled, the hardened bisqueformed powders can be removed for further HPHT processing. A bisque formof feedstock 1003 is the net product.

FIG. 11 shows fabrication 1110 of a bisque form for a full hemisphericalpart 1109 that has multiple powder layers 1107 a and 1107 b. Pre-mixedpowders of PDC, PCBN, ceramic, or cermet materials that contain enoughmetal to undergo solid phase sintering are loaded into the bisquingmolds or containers 1108. A release agent may be required between themold/container to ensure that the final bisque form can be removedfollowing furnace firing. The bisque mold/container assembly may then beplaced in a vacuum furnace that is drawn to a vacuum ranging from 200 to0 Militorrs. The load is then heated within a range of 0.6 to 0.8 of themelting temperature of the largest volume mix metal. Once the furnacecycle is completed and the mold/container is cooled, the hardened bisque1109 formed powders can be removed for further HPHT processing. Anexample of a bisque binder burn-out cycle that may be used to remove theunwanted materials before sintering is as follows:

Time Temperature (hours) (degrees Centigrade) 0 21 0.25 21 5.19 800 6.19800 10.19 21Reduction of Free Volume in Diamond Feedstock

As mentioned earlier, it may be desirable to remove free volume in thediamond feedstock before sintering is attempted. The inventors havefound this is a useful procedure when producing non-planar concave andconvex parts. If a press with sufficient anvil travel is used for highpressure and high temperature sintering, however, this step may not benecessary. Free volume in the diamond feedstock will be reduced so thatthe resulting diamond feedstock is at least about 95% theoreticaldensity and closer to about 97% of theoretical density.

Referring to FIGS. 1 GA and 1G, an assembly used for precompressingdiamond to eliminate free volume is depicted. In the drawing, thediamond feedstock is intended to be used to make a convex non-planarpolycrystalline diamond part. The assembly may be adapted forprecompressing diamond feedstock for making PDCs of other complexshapes.

The assembly depicted includes a cube 161 of a pressure transfer medium.A cube is made from pyrophillite or other appropriate pressure transfermaterial such as a synthetic pressure medium and is intended to undergopressure from a cubic press with anvils simultaneously pressing the sixfaces of the cube. A cylindrical cell rather than a cube may be used ifa belt press is utilized for this step.

The cube 161 has a cylindrical cavity 162 or passage through it. Thecenter of the cavity 162 will receive a non-planar refractory metal can170 loaded with diamond feedstock 166 that is to be precompressed. Thediamond feedstock 166 may have a substrate with it.

The can 170 consists of two non-planar can halves 170 a and 170 b, oneof which overlaps the other to form a slight lip 172. The can may be anappropriate refractory metal such as niobium, tantalum, molybdenum, etc.The can is typically two hemispheres, one that is slightly larger toaccept the other being slid inside of it to fully enclosed the diamondfeedstock. A rebated area or lip is provided in the larger can so thatthe smaller can will satisfactorily fit therein. The seam of the can issealed with an appropriate sealant such as dry hexagonal boronitride ora synthetic compression medium. The sealant forms a barrier thatprevents the salt pressure medium from penetrating the can. The can seammay also be welded by plasma, laser, or electron beam processes.

An appropriately shaped pair of salt domes 164 and 167 surround the can170 containing the diamond feedstock 166. In the example shown, the saltdomes each have a non-planar cavity 165 and 168 for receiving the can170 containing the non-planar diamond feedstock 166. The salt domes andthe can and diamond feedstock are assembled together so that the saltdomes encase the diamond feedstock. A pair of cylindrical salt disks 163and 169 are assembled on the exterior of the salt domes 164 and 167. Allof the aforementioned components fit within the bore 162 of the pressuremedium cube 161.

The entire pyrocube assembly is placed into a press and pressurizedunder appropriate pressure (such as about 40-68 Kbar) and for anappropriate although brief duration to precompress the diamond andprepare it for sintering. No heat is necessary for this step.

Mold Releases

When making non-planar shapes, it may be desirable to use a mold in thesintering process to produce the desired net shape. CoCr metal may usedas a mold release in forming shaped diamond or other superhard products.Sintering the superhard powder feed stocks to a substrate, the object ofwhich is to lend support to the resulting superhard table, may beutilized to produce standard PDC and PCBN parts. However, in someapplications, it is desired to remove the diamond table from thesubstrate.

Referring to FIG. 14, a diamond layer 1402 and 1403 has been sintered toa substrate 1401 at an interface 1404. The interface 1404 must be brokento result in free standing diamond if the substrate is not required inthe final product. A mold release may be used to remove the substratefrom the diamond table. If CoCr alloy is used for the substrate, thenthe CoCr itself serves as a mold release, as well as serving as asolvent-catalyst metal. CoCr works well as a mold release because itsCTE is dramatically different than that of sintered PDC or PCBN. Becauseof the large disparity in the CTEs between PDC and PCBN and CoCr, highstress is formed at the interface 1501 between these two materials asshown in FIG. 15. The stress that is formed is greater than the bondenergy between the two materials. When the stress is greater than thebond energy, a crack is formed at the point of highest stress. The crackthen propagates following the narrow region of high stress concentratedat the interface. Referring to FIG. 16, in this way, the CoCr substrate1601 will separate from the PCD or PCBN 1602 that was sintered aroundit, regardless of the shape of the interface.

Materials other than CoCr can be used as a mold release. These materialsinclude those metals with high CTEs and, in particular, those that arenot good carbide formers. These are, for example, Co, Ni, CoCr, CoFe,CoNi, Fe, steel, etc.

Gradient Layers and Stress Modifiers

Gradient layers and stress modifiers may be used in the making ofsuperhard constructs. Gradient layers may be used to achieve any of thefollowing objectives:

A. Improve the “sweep” of solvent metal into the outer layer ofsuperhard material and to control the amount of solvent metal introducedfor sintering into the outer layer.

B. Provide a “sweep” source to flush out impurities for deposit on thesurface of the outer layer of superhard material and/or chemicalattachment/combination with the refractory containment cans.

C. Control the Bulk Modulus of the various gradient layers and therebycontrol the overall dilatation of the construct during the sinteringprocess.

D. Affect the CTE of each of the various layers by changing the ratio ofmetal or carbides to diamond, PCBN or other Superhard materials toreduce the CTE of an individual gradient layer.

E. Allow for the control of structural stress fields through the variouslevels of gradient layers to optimize the overall construct.

F. Change the direction of stress tensors to improve the outer Superhardlayer, e.g., direct the tensor vectors toward the center of a sphericalconstruct to place the outer layer diamond into compression, orconversely, direct the tensor vectors from the center of the constructto reduce interface stresses between the various gradient layers.

G. Improve the overall structural stress compliance to external orinternal loads by providing a construct that has substantially reducedbrittleness and increased toughness wherein loads are transferredthrough the construct without crack initiation and propagation.

Referring to FIG. 17, the liquid sintering phase of PDC and PCBN istypically accomplished by mixing the solvent sintering metal 1701directly with the diamond or PCBN powders 1702 prior to the HPHTpressing, or (referring to FIG. 18) “sweeping” the solvent metal 1802from a substrate 1801 into feedstock powders from the adjacent substrateduring HPHT. High quality PDC or PCBN is created using the “sweep”process.

There are several theories related to the increased PDC and PCBN qualitywhen using the sweep method. However, most of those familiar with thefield agree that allowing the sintering metal to “sweep” from thesubstrate material provides a “wave front” of sintering metal thatquickly “wets” and dissolves the diamond or CBN and uses only as muchmetal as required to precipitate diamond or PCBN particle-to-particlebonding. Whereas in a “premixed” environment the metal “blinds off” theparticle-to particle reaction because too much metal is present, orconversely, not enough metal is present to ensure the optimal reaction.

Furthermore, it is felt that the “wave front” of metal sweeping throughthe powder matrix also carries away impurities that would otherwiseimpede the formation of high quality PDC of PCBN. These impurities arenormally “pushed” ahead of the sintering metal “wave front” and aredeposited in pools adjacent to the refractory containment cans. FIG. 19depicts the substrate 1904, the wavefront 1903, and the feedstockcrystals or powder 1902 that the wavefront will sweep through 1901.Certain refractory material such as Niobium, Molybdenum, and Zirconiumcan act as “getters” that combine with the impurities as they immergefrom the matrix giving additional assistance in the creation of highquality end products.

While there are compelling reasons to use the “sweep” process insintering PDC and PCBN there are also problems that arise out of itsuse. For example, not all substrate metals are as controllable as othersas to the quantity of material that is delivered and ultimately utilizedby the powder matrix during sintering. Cobalt metal (6 to 13% by volume)sweeping from cemented tungsten carbide is very controllable when usedagainst diamond or PCBN powders ranging from 1 to 40 microns particlesized. On the other hand, cobalt chrome molybdenum (CoCrMo) that isuseful as a solvent metal to make PDC for some applications overwhelmsthe same PDC matrix with CoCrMo metal in a pure sweep process sometimesproducing inferior quality PDC. The fact that the CoCrMo has a lowermelting point than cobalt, and further that there is an inexhaustiblesupply when using a solid CoCrMo substrate adjacent to the PDC matrix,creates a non-controllable processing condition.

In some applications where it is necessary to use sintering metals sucha CoCrMo that can not be “swept” from a cemented carbide product, it isnecessary to provide a simulated substrate against the PDC powders thatprovides a controlled release and limited supply of CoCrMo for theprocess.

These “simulated”i substrates have been developed in the forms of“gradient” layers of mixtures of diamond, carbides, and metals toproduce the desired “sweep” affect for sintering the outer layer of PDC.The first “gradient layer” Oust adjacent to the outer or primary diamondlayer which will act as the bearing or wear surface) can be preparedusing a mixture of diamond, Cr₃C₂, and CoCrMo. Depending on the sizefraction of the diamond powder used in the outer layer, the firstgradient layers diamond size fraction and metal content is adjusted forthe optimal sintering conditions.

Where a “simulated” substrate is used, it has been discovered that oftena small amount of solvent metal, in this case CoCrMo must be added tothe outside diamond layer as catalyst to “kick-off” the sinteringreaction.

One embodiment utilizes the mix ranges for the outer 2001 and inner 2002gradient layers of FIG. 20 that are listed in Table 9.

TABLE 9 DIAMOND DIAMOND Cr₃C₂ GRADIENT (Vol. (Size Fraction- (Vol.CoCrMo LAYERS Percent) μm) Percent) (Vol. Percent) Outer 92 25 0 8 Inner70 40 10 20

The use of gradient layers with solid layers of metal allows thedesigner to match the bulk modulus to the CTE of various features of theconstruct to counteract dilatory forces encountered during the HTHPphase of the sintering process. For example, in a spherical construct asthe pressure increases the metals in the construct are compressed ordilated radially toward the center of the sphere. Conversely, as thesintering temperature increases the metal expands radially away from thecenter of the sphere. Unless these forces are balanced in some way, thecompressive dilatory forces will initiate cracks in the outer diamondlayer and cause the construct to be unusable.

Typically, changes in bulk modulus of solid metal features in theconstruct are controlled by selecting metals with a compatible modulusof elasticity. The thickness and other sizing features are alsoimportant. CTE, on the other hand, is changed by the addition of diamondor other carbides to the gradient layers.

One embodiment, depicted in FIG. 21, involves the use of two gradientouter layers 2101 and 2102, a solid titanium layer 2104 and an innerCoCrMo sphere 2103. In this embodiment the first gradient layer providesa “sweep source” of biocompatible CoCrMo solvent metal to the outerdiamond layer. The solid titanium layer provides a dilatory source thatoffsets the CTE from the solid CoCrMo center ball and keeps it from“pulling away” from the titanium/CoCrMo interface as the sinteringpressure and temperature go from the 65 Kbar and 1400° C. sinteringrange to 1 bar and room temperature.

Where two or more powder based gradient layers are to be used in theconstruct it becomes increasingly important to control the CTE of eachlayer to ensure structural integrity following sintering. During thesintering process stresses are induced along the interface between eachof the gradient layers. These high stresses are a direct result of thedifferences in the CTE between any two adjacent layers. To reduce thesestresses the CTE of one or both of the layer materials must be modified.

The CTE of the a substrate can be modified by either changing to asubstrate with a CTE close to that of diamond (an example is the use ofcemented tungsten carbide, where the CTE of diamond is approximately 1.8μm/m-° C. and cemented tungsten carbide is approximately 4.4 μm/m-° C.),or in the case of powdered layers, by adding a low CTE material to thesubstrate layer itself. That is, making a mixture of two or morematerials, one or more of which will alter the CTE of the substratelayer.

Metal powders can be mixed with diamond or other superhard materials toproduce a material with a CTE close to that of diamond and thus producestresses low enough following sintering to prevent delamination of thelayers at their interfaces. Experimental data shows that the CTEaltering materials will not generally react with each other, whichallows the investigator to predict the outcome of the intermediate CTEfor each gradient level.

The desired CTE is obtained by mixing specific quantities of twomaterials according to the rule of mixtures. Table 10 shows the changein CTE between two materials, A and B as a function of composition(volume percent). In this example, materials A and B have CTEs of 150and 600 μIn./In.-° F. respectively. By adding 50 mol % of A to 50 mol %of B the resulting CTE is 375 μin/in-° F.

One or more of the following component processes is incorporated intothe mold release system:

1. An intermediate layer of material between the PDC part and the moldthat prevents bonding of the polycrystalline diamond compact to the moldsurface.

2. A mold material that does not bond to the PDC under the conditions ofsynthesis.

3. A mold material that, in the final stages of, or at the conclusionof, the PDC synthesis cycle either contracts away from the PDC in thecase of a net concave PDC geometry, or expands away from the PDC in thecase of a net convex PDC geometry.

4. The mold shape can also act simultaneously as a source of sweep metaluseful in the PDC synthesis process.

As an example, a mold release system may be utilized in manufacturing aPDC by employing a negative shape of the desired geometry to producenon-planar parts. The mold surface contracts away from the final netconcave geometry, the mold surface acts as a source of solvent-catalystmetal for the PDC synthesis process, and the mold surface has poorbonding properties to PDCs.

TABLE 10 PREDICTED DIMENSIONAL CHANGES IN AN EIGHT INCH LAYEREDCONSTRUCT Final CTE Total Length Dimension A % B % (μ In./In-° F.)Change (In.) (In.) 100 0 150 .0012 7.9988 90 10 195 .0016 7.9984 80 20240 .0019 7.9981 70 30 285 .0023 7.9977 60 40 330 .0026 7.9974 50 50 375.0030 7.9970 40 60 420 .0034 7.9966 30 70 465 .0037 7.9963 20 80 510.0041 7.9959 10 90 555 .0044 7.9956 0 100 600 .0048 7.9952

FIG. 22 is an illustration of how the above CTE modification works in aone-dimensional example. The one-dimensional example works as well in athree-dimensional construct. If the above materials A and B are packedin alternating layers 2201 and 2202 as shown in FIG. 22, separately intheir pure forms, with their CTEs of 150 and 600 μIn./In.-° F.respectively, they will contract exactly 150 μIn./In.-° F. and 600μIn./In.-° F. for every degree decrease in temperature. For an eightinch block of one inch thick stacked layers the total change indimension for a one degree decrease in temperature will be:

Material A: (4×1 In.)×(0.00015 In./In.-° F.)×1° F.=0.0006 In.

Material B: (4×1 In.)×(0.00060 In./In.-° F.)×1)° F.=0.0024 In.

Total overall length decrease in eight inches=0.0030 In.

By comparison, each of the layers is modified by using a mixture of 50%of A and 50% of B, and all eight layers are stacked into the eight-inchblock configuration. Re-calculation of the overall length decrease usingthe new composite CTE of 375 μIn./In.-° F. from Table II shows:

Material A+B: (8×1 In.)×(0.000375 In./In.-° F.)×1° F.=0.0030 In.

Total overall length decrease in eight inches=0.0030 In.

The length decrease in this case was accurately predicted for theone-dimensional construct using one-inch thick layers by using the ruleof mixtures.

Metals have very high CTE values as compared to diamond, which has oneof the lowest CTEs of any known material. When metals are used assubstrates for PDC and PCBN sintering considerable stress is developedat the interface. Therefore, mixing low CTE material with thebiocompatible metal for medical implants can be used to reduceinterfacial stresses. One of the best candidate materials is diamonditself. Other materials include refractory metal carbides and nitrides,and some oxides. Borides and silicides would also be good materials froma theoretical standpoint, but may not be biocompatible. The following isa list of candidate materials:

Carbides Silicides Oxynitrides Nitrides Oxides Oxyborides BoridesOxycarbides Carbonitrides

There are other materials and combinations of materials that could beutilized as CTE modifiers.

There are also other factors that apply to the reduction of interfacestresses for a particular geometrical construct. The thickness of thegradient layer, its position in the construct, and the general shape ofthe final construct all contribute in interfacial stress tensorreduction. Geometries that are more spherical tend to promote interfacecircumferential failures from positive or negative radial tensors whilegeometries of a cylindrical configuration tend to fail at the layerinterfaces precipitated by bending stress couples.

The design of the gradient layers respecting CTE and the amount ofcontraction that each individual layer will experience during coolingform the HTHP sintering process will largely dictate the direction ofstress tensors in the construct. Generally, the designer will alwaysdesire to have the outer wear layer of superhard material in compressionto prevent delamination and crack propagation. In spherical geometriesthe stress tensors would be directed radially toward the center of thespherical shape giving special attention to the interfacial stresses ateach layer interface to prevent failures at these interfaces as well. Incylindrical geometries the stress tensors would be adjusted to preventstress couples from initiating cracks in either end of the cylinder,especially at the end where the wear surface is present.

The following are embodiments that relate to a spherical geometrywherein combinations of gradient layers and/or solid metal balls areused to control the final outcomes of the constructs. FIG. 23 is anembodiment that shows a spherical construct, which utilizes fivegradient layers wherein the composition of each layer is described inTables 11 and 12:

TABLE 11 DIAMOND LAYER Size Cr3C2 CoCrMo THICKNESS LAYER (μm) Volume %Volume % Volume % (In.) First (Outer 20 92 8 0 .090 Layer) 2301 Second2302 40 70 20 20 .104 Third 2303 70 60 20 20 .120 Forth 2304 70 60 26 26.138 Fifth 2305 70 25 37.5 37.5 .154

TABLE 12 DIAMOND LAYER Size Cr3C2 CoCrMo THICKNESS LAYER (μm) Volume %Volume % Volume % (In.) First 20 100 0 0 .090 (Outer Layer) 2301 Second2302 40 70 20 20 .104 Third 2304 70 60 20 20 .120 Forth 2304 70 60 26 26.138 Fifth 2305 70 25 37.5 37.5 .154

FIG. 24 is an embodiment that shows a spherical construct, whichutilizes four gradient layers wherein the composition of each layer isdescribed in Tables 13 and 14.

TABLE 13 DIAMOND LAYER Size Volume Cr3C2 CoCrMo THICKNESS LAYER (μm) %Volume % Volume % (In.) First 20 92 0 8 .097 (Outer Layer) 2401 Second40 70 10 20 .125 2402 Third 70 60 20 20 .144 2403 Forth 70 50 25 25 .2402404

TABLE 14 DIAMOND LAYER Size Cr3C2 CoCrMo THICKNESS LAYER (μm) Volume %Volume % Volume % (In.) First 20 100 0 0 .097 (Outer Layer) 2401 Second2402 40 70 10 20 .125 Third 2403 70 60 20 20 .144 Forth 2404 70 50 25 25.240

FIG. 25 shows an embodiment construct that utilizes a center supportball with gradient layers laid up on the ball and each other to form thecomplete construct. The inner ball of solid metal CoCrMo is encapsulatedwith a 0.003 to 0.010 inch thick refractory barrier can 2504 to preventthe over saturation of the system with the ball metal during the HTHPphase of sintering. The composition of each layer is described in Tables15 and 16.

TABLE 15 DIAMOND LAYER Size Cr3C2 CoCrMo THICKNESS LAYER (μm) Volume %Volume % Volume % (In.) First 20 92  0  8 .097 (Outer Layer) 2501 Second2502 40 70 10 20 .125 Third 2503 70 60 20 20 .144 CoCrMo N/A N/A N/A N/AN/A Ball 2505

TABLE 16 DIAMOND LAYER Size Cr3C2 CoCrMo THICKNESS LAYER (μm) Volume %Volume % Volume % (In.) First 20 100 0 0 .097 (Outer Layer) 2501 Second2502 40 70 10 20 .125 Third 2503 70 60 20 20 .144 CoCrMo N/A N/A N/A N/AN/A Ball 2505

Predicated on the end use function of the sphere above, the inner ballmay be made of cemented tungsten carbide, niobium, nickel, stainlesssteel, steel, or one of several other metal or ceramic materials to suitthe designers needs.

Embodiments relating to dome shapes are described as follow:

FIG. 26 shows a dome embodiment construct that utilizes two gradientlayers 2601 and 2602 wherein the composition of each layer is describedin Tables 17 and 18.

TABLE 17 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 94 0 6 0.05 .200(Outer Layer) 2602 Second 2601 70 60 20 20 0.05 .125

TABLE 18 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .200(Outer Layer) 2602 Second 2601 70 60 20 20 0.05 .125

FIG. 27 shows a dome embodiment construct that utilizes two gradientlayers 2701 and 2702 wherein the composition of each layer is describedin Tables 19 and 20:

TABLE 19 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 94 0 6 0.05 .128(Outer Layer) 2702 Second 2701 70 60 20 20 0.05 .230

TABLE 20 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .128(Outer Layer) 2702 Second 2701 70 60 20 20 0.05 .230

FIG. 28 shows a dome embodiment construct that utilizes three gradientlayers 2801, 2802 and 2803 where the composition of each layer isdescribed in Tables 21 and 22:

TABLE 21 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 96 0 4 0.05 .168(Outer Layer) 2801 Second 2802 40 80 10 10 0.05 .060 Third 2803 70 60 2020 0.05 .130

TABLE 22 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .168(Outer Layer) 2801 Second 2802 40 80 10 10 0.05 .060 Third 2803 70 60 2020 0.05 .130

FIG. 29 shows a dome embodiment construct that utilizes three gradientlayers 2901, 2902 and 9803 wherein the composition of each layer isdescribed in Tables 23 and 24.

TABLE 23 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 96 0 4 0.05 .065(Outer Layer) 2901 Second 2902 40 80 10 10 0.05 .050 Third 2903 70 60 2020 0.05 .243

TABLE 24 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .065(Outer Layer) 2901 Second 2902 40 80 10 10 0.05 .050 Third 2903 70 60 2020 0.05 .243

Embodiments relating to Flat Cylindrical shapes are described asfollows:

FIG. 30 shows a flat cylindrical embodiment construct that utilizes twogradient layers 3001 and 3002 wherein the composition of each layer isdescribed in Tables 25 and 26.

TABLE 25 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 94 0 6 0.05 (OuterLayer) 3001 Second 3002 70 60 20 20 0.05

TABLE 26 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 (OuterLayer) 3001 Second 3002 70 60 20 20 0.05

FIG. 31 shows a flat cylindrical embodiment construct that utilizesthree gradient layers 3101, 3102, 3103 wherein the composition of eachlayer is described in Tables 27 and 28:

TABLE 27 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 96 0 4 0.05 (OuterLayer) 3101 Second 3102 40 80 10 10 0.05 Third 3103 70 60 20 20 0.05

TABLE 28 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 (OuterLayer) 3101 Second 3102 40 80 10 10 0.05 Third 3103 70 60 20 20 0.05

FIG. 32 shows a flat cylindrical embodiment construct that utilizesthree gradient layers 3201, 3202, 3203 laid up on a CoCrMo substrate3204. The cylindrical substrate of solid metal CoCrMo 3204 isencapsulated with a 0.003 to 0.010 inch thick refractory barrier can3205 to prevent the over saturation of the system with the substratemetal during the HTHP phase of sintering. The composition of each layeris described in Tables 29 and 30:

TABLE 29 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 96 0 4 0.05 (OuterLayer) 3201 Second 3202 40 80 10 10 0.05 Third 3203 70 60 20 20 0.05CoCrMo N/A N/A N/A N/A N/A Substrate 3204

TABLE 30 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 (OuterLayer) 3201 Second 3202 40 80 10 10 0.05 Third 3203 70 60 20 20 0.05CoCrMo N/A N/A N/A N/A N/A Substrate 3204

Predicated on the end use function of the cylinder shape of FIG. 32 theinner substrate could be made of cemented tungsten carbide, niobium,nickel, stainless steel, steel, or one of several other metal or ceramicmaterials to suite the designers needs.

Embodiments relating to flat cylindrical shapes with formed-in-placeconcave features are described as follow:

FIG. 33 shows an embodiment of a flat cylindrical shape with a formed inplace concave trough or filler support 3303 that utilizes two gradientlayers 3301 and 3302 wherein the composition of each layer is describedin Tables 31 and 32:

TABLE 31 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 94 0 6 0.05 .156(Outer Layer) 3301 Second 3302 70 60 20 20 0.05 .060 Filler Support 7060 20 20 0.05 N/A 3303

TABLE 32 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .156(Outer Layer) 3301 Second 3302 70 60 20 20 0.05 .060 Filler Support 7060 20 20 0.05 N/A 3303

FIG. 34 shows an embodiment of a flat cylindrical shape with a formed inplace concave trough or filler support 3403 that utilizes two gradientlayers 3401 and 3402 wherein the composition of each layer is describedin Tables 33 and 34:

TABLE 33 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 94 0 6 0.05 .156(Outer Layer) 3401 Second 3402 70 60 20 20 0.05 .060 Filler Support 7060 20 20 0.05 N/A 3403

TABLE 34 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .156(Outer Layer) 3401 Second 3402 70 60 20 20 0.05 .060 Filler Support 7060 20 20 0.05 N/A 3403

FIG. 35 shows an embodiment of a flat cylindrical shape with a formed inplace concave trough or filler support 3504 that utilizes three gradientlayers 3501, 3502, 3503 wherein the composition of each layer isdescribed in Tables 35 and 36:

TABLE 35 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 96 0 4 0.05 .110(Outer Layer) 3501 Second 3502 40 80 10 10 0.05 .040 Third 3503 70 60 2020 0.05 .057 Filler Support 70 60 20 20 0.05 N/A 3504

TABLE 36 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .110(Outer Layer) 3501 Second 3502 40 80 10 10 0.05 .040 Third 3503 70 60 2020 0.05 .057 Filler Support 70 60 20 20 0.05 N/A 3504

FIG. 36 shows an embodiment of a flat cylindrical shape with a formed inplace concave trough or filler support 3604 that utilizes three gradientlayers 3601, 3602, 3603 wherein the composition of each layer isdescribed in Tables 37 and 38:

TABLE 37 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 96 0 4 0.05 .110(Outer Layer) 3601 Second 3602 40 80 10 10 0.05 .040 Third 3603 70 60 2020 0.05 .057 Filler Support 70 60 20 20 0.05 N/A 3604

TABLE 38 DIAMOND LAYER Size Cr3C2 CoCrMo TiCTiN THICKNESS LAYER (μm)Volume % Volume % Volume % Volume % (In.) First 20 100 0 0 0.05 .110(Outer Layer) 3601 Second 3602 40 80 10 10 0.05 .040 Third 3603 70 60 2020 0.05 .057 Filler Support 70 60 20 20 0.05 N/A 3604Prepare Heater Assembly

In order to sinter the assembled and loaded diamond feedstock describedabove into PCD, both heat and pressure are required. Heat is providedelectrically as the part undergoes pressure in a press. A heaterassembly is used to provide the required heat.

A refractory metal can containing loaded and precompressed diamondfeedstock is placed into a heater assembly. Salt domes are used toencase the can. The salt domes used may be white salt (NaCl) that isprecompressed to at least about 90-95% of theoretical density. Thisdensity of the salt is desired to preserve high pressures of thesintering system and to maintain geometrical stability of themanufactured part. The salt domes and can are placed into a graphiteheater tube assembly. The salt and graphite components of the heaterassembly may be baked in a vacuum oven at greater than 100 degreesCelsius and at a vacuum of at least 23 torr for about 1 hour in order toeliminate absorbed water prior to loading in the heater assembly. Othermaterials that may be used in construction of a heater assembly includesolid or foil graphite, amorphous carbon, pyrolitic carbon, refractorymetals and high electrical resistant metals.

Once electrical power is supplied to the heater tube, it will generateheat required for polycrystalline diamond formation in the highpressure/high temperature pressing operation.

Preparation of Pressure Assembly for Sintering

Once a heater assembly has been prepared, it is placed into a pressureassembly for sintering in a press under high pressure and hightemperature. A cubic press or a belt press may be used for this purpose,with the pressure assembly differing somewhat depending on the type ofpress used. The pressure assembly is intended to receive pressure from apress and transfer it to the diamond feedstock so that sintering of thediamond may occur under isostatic conditions.

If a cubic press is used, then a cube of suitable pressure transfermedia such as pyrophillite will contain the heater assembly. Cellpressure medium may be used if sintering is to take place in a beltpress. Salt may be used as a pressure transfer media between the cubeand the heater assembly. Thermocouples may be used on the cube tomonitor temperature during sintering. The cube with the heater assemblyinside of it is considered a pressure assembly, and is place into apress a press for sintering.

Sintering of Feedstock into PCD

The pressure assembly described above containing a refractory metal canthat has diamond feedstock loaded and precompressed within is placedinto an appropriate press. An appropriate press is used to create hightemperature and high pressure conditions for sintering.

To prepare for sintering, the entire pressure assembly is loaded into acubic press and initially pressurized to about 40-68 Kbars. The pressureto be used depends on the product to be manufactured and must bedetermined empirically. Then electrical power is added to the pressureassembly in order to reach a temperature in the range of less than about1145 or 1200 to more than about 1500 degrees Celsius. About 5800 wattsof electrical power is available at two opposing anvil faces, creatingthe current flow required for the heater assembly to generate thedesired level of heat. Once the desired temperature is reached, thepressure assembly is subjected to pressure of about 1 million pounds persquare inch at the anvil face. The components of the pressure assemblytransmit pressure to the diamond feedstock. These conditions aremaintained for about 3-12 minutes, but could be from less than 1 minuteto more than 30 minutes. The sintering of PDCs takes place in anisostatic environment where the pressure transfer components arepermitted only to change in volume but are not permitted to otherwisedeform. Once the sintering cycle is complete, about a 90 second cooldown period is allowed, and then pressure is removed. The PDC is thenremoved for finishing.

Removal of a sintered PDC having a curved, compound or complex shapefrom a pressure assembly is simple due to the differences in materialproperties between diamond and the surrounding metals in someembodiments. This is generally referred to as the mold release system.

Removal of Solvent-Catalyst Metal from PCD

If desired, the solvent-catalyst metal remaining in interstitial spacesof the sintered PCD may be removed. Such removal is accomplished bychemical leaching as is known in the synthetic diamond field. Aftersolvent-catalyst metal has been removed from the interstitial spaces inthe diamond table, the diamond table will have greater stability at hightemperatures. This is because there is no catalyst for the diamond toreact with and break down.

After leaching solvent-catalyst metal from the diamond table, it may bereplaced by another metal or metal compound to form thermally stablediamond that is stronger than leached PCD. If it is intended to weldsynthetic diamond or a PDC to a substrate or to another surface such asby inertia welding, it may be desirable to use thermally stable diamonddue to its resistance to heat generated by the welding process.

Manufacture of Concave Surfaces

An example substrate geometry for manufacturing a concave spherical,hemispherical or partially spherical polycrystalline diamond compact canbe understood in conjunction with review of FIGS. 37A-37C. The substrate601 (and 601 a and 601 b) may be in the form of a cylinder with ahemispherical receptacle 602 (and 602 a and 602 b) formed into one ofits ends. Two substrate cylinders 601 a and 601 b are placed so thattheir hemispherical receptacles 602 a and 602 b are adjacent each other,thus forming a spherical cavity 604 between them. A sphere 603 of anappropriate substrate material is located in the cavity 604. Diamondfeedstock 605 is located in the cavity 604 between the exterior of thesphere 603 and the concave surfaces of the receptacles 602 a and 602 bof the substrate cylinders 601 a and 601 b. The assembly is placed intoa refractory metal can 610 for sintering. The can has a first cylinder610 a and a second cylinder 601 b. The two cylinders join at a lip 611.After such an assembly is sintered, the assembly may be slit, cut orground along the center line 606 in order to form a first cup assembly607 a and a second cup assembly 607 b. Example substrate materials forthe cylinders 602 a and 602 b are CoCrMo (ASTM F-799) and CoCrW (ASTMF-90), and an example substrate material for the sphere 603 is CoCrMo(ASTM F-799), although any appropriate substrate material may be used,including some of those listed elsewhere herein.

Manufacture of Convex Surfaces

In this section, examples for manufactureing various convex superhardsurfaces are provided. Referring to FIGS. 13A-13F, various substratestructures of the invention for making a generally sphericalpolycrystalline diamond or polycrystalline cubic boron nitride compactare depicted. FIGS. 13A and 13B depict two-layer substrates.

In FIG. 13A, a solid first sphere 501 of a substrate material intendedto be used as the substrate shell or outer layer was obtained. Thedimensions of the first sphere 501 are such that the dimension of thefirst sphere 501 with a diamond table on its exterior will approximatethe intended dimension of the component prior to final finishing. Oncethe first sphere 501 of the substrate is obtained, a hole 502 is boredinto its center. The hole 502 is preferably bored, drilled, cut, blastedor otherwise formed so that the terminus 503 of the hole 502 ishemispherical. This may be achieved by using a drill bit or end millwith a round or ball end having the desired radius and curvature. Then asecond sphere 504 of a substrate material is obtained. The second sphere504 is smaller than the first sphere 501 and is be placed in hole 502 inthe first sphere 501. The substrates materials of spheres 501 and 504may be selected form those listed in the tables above. They may also beof other appropriate materials. The second sphere 504 and the hole 502and its terminus 503 should fit together closely without excessivetolerance or gap. A plug 505 which may be of the same substrate materialas first sphere 501 is formed or obtained. The plug 505 has a first end505 a and a second end 505 b and substrate material therebetween inorder to fill the hole 502 except for that portion of the hole 502occupied by the second sphere 504 adjacent the hole terminus 503. Theplug 505 may have a concave hemispherical receptacle 506 at its firstend 505 a so that plug 505 will closely abut second sphere 504 acrossabout half the spherical surface of second sphere 504. The plug 505 maybe generally cylindrical in shape. The substrate assembly including onesubstrate sphere placed inside of another may then be loaded withdiamond feedstock 507 or cubic boron nitride feedstock and sinteredunder high pressure at high temperature to form a sphericalpolycrystalline diamond compact.

Referring to FIG. 13B, another substrate geometry for manufacturingspherical polycrystalline diamond or cubic boron nitride compacts isdepicted. An inner core sphere 550 of appropriate substrate material isselected. Then an outer substrate first hemisphere 551 and outersubstrate second hemisphere 552 are selected. Each of the outersubstrate first and second hemispheres 551 and 552 are formed so thatthey each have a hemispherical receptacle 551 a and 552 a shaped andsized to accommodate placement of the hemispheres about the exterior ofthe inner core sphere 550 and thereby enclose and encapsulate the innercore sphere 550. The substrates materials of inner core sphere 550 andhemispheres 551 and 552 are preferably selected form those listed in thetables above or other appropriate materials. With the hemispheres andinner core sphere assembled, diamond feedstock 553 may be loaded aboutthe exterior of the hemispheres and high temperature and high pressuresintering may proceed in order to form a spherical compact.

Although FIGS. 13A and 13B depict two-layer substrates, it is possibleto use multiple layer substrates (3 or more layers) for the manufactureof polycrystalline diamond or polycrystalline diamond compacts orpolycrystalline cubic boron nitride compacts. The selection of asubstrate material, substrate geometry, substrate surface topographicalfeatures, and substrates having a plurality of layers (2 or more layers)of the same or different materials depend at least in part on thethermo-mechanical properties of the substrate, the baro-mechanicalproperties of the substrate, and the baro-mechanical properties of thesubstrate.

Referring to FIG. 13C, another substrate configuration for makinggenerally spherical compacts is depicted. The substrate 520 is in thegeneral form of a sphere. The surface of the sphere includes substratesurface topography intended to enhance fixation of a diamond table tothe substrate. The substrate has a plurality of depressions 521 formedon its surface. Each depression 521 is formed as three different levelsof depression 521 a, 521 b and 521 c. The depressions are depicted asbeing concentric circles, each of approximately the same depth, buttheir depths could vary, the circles need not be concentric, and theshape of the depressions need not be circular. The depression walls 521d, 521 e and 521 f are depicted as being parallel to a radial axis ofthe depressions which axis is normal to a tangent to the theoreticalspherical extremity of the sphere, but could have a differentorientation if desired. As depicted, the surface of the substrate sphere522 has no topographical features other than the depressions alreadymentioned, but could have protrusions, depressions or othermodifications as desired. The width and depth dimensions of thedepressions 521 may be varied according to the polycrystalline diamondcompact that is being manufactured. Diamond feedstock may be loadedagainst the exterior of the substrate sphere 520 and the combination maybe sintered at diamond stable pressures to produce a sphericalpolycrystalline diamond compact. Use of substrate surface topographicalfeatures on a generally spherical substrate provides a superior bondbetween the diamond table and the substrate as described above andpermits a polycrystalline diamond compact to be manufactured using asingle layer substrate. That is because of the gripping action betweenthe substrate and the diamond table achieved by use of substrate surfacetopographical features.

Referring to FIG. 13D, a segmented spherical substrate 523 is depicted.The substrate has a plurality of surface depressions 524 equally spacedabout its exterior surface. These depressions as depicted are formed inlevels of three different depths. The first level 524 a is formed to apredetermined depth and is of pentagonal shape about its outerperiphery. The second level 524 b is round in shape and is formed to apredetermined depth which may be different from the predetermined depthof the pentagon. The third level 524 c is round in shape in is formed toa predetermined depth which may be different from each of the otherdepths mentioned above. Alternatively, the depressions may be formed toonly one depth, may all be pentagonal, or may be a mixture of shapes.The depressions may be formed by machining the substrate sphere.

Referring to FIG. 13E, a cross section of an alternative substrateconfiguration for making a polycrystalline diamond or polycrystallinecubic boron nitride compact is shown. A compact 525 is shown. Thecompact 525 is spherical. The compact 525 includes a diamond table 526sintered to a substrate 527. The substrate is partially spherical inshape at its distal side 527 a and is dome-shaped on its proximal side527 b. Alternatively, the proximal side 527 b of the substrate 527 maybe described as being partially spherical, but the sphere on which it isbased has a radius of smaller dimension than the radius of the sphere onwhich the distal side 527 a of the substrate is based. Each of the top527 c and bottom 527 d are formed in a shape convenient to transitionfrom the proximal side 527 b substrate partial sphere to the distal side527 a substrate partial sphere. This substrate configuration hasadvantages in that it leaves a portion of substrate exposed for drillingand attaching fixation components without disturbing residual stressfields of the polycrystalline diamond table. It also provides a portionof the substrate that does not have diamond sintered to it, allowingdilatation of the substrate during sintering without disruption of thediamond table. More than 180 degrees of the exterior of the substratesphere has diamond on it, however, so the part is useful as a femoralhead or other articulation surface.

Referring to FIG. 13F, a cross section of an alternative substrateconfiguration for making a polycrystalline diamond compact is shown. Apolycrystalline diamond compact 528 is depicted having a diamond table529 and a substrate 530. The substrate has topographical features 531for enhancing strength of the diamond to substrate interface. Thetopographical features may include rectangular protrusions 532 spacedapart by depressions 533 or corridors. The distal side of the substrateis formed based on a sphere of radius r. The proximal side of thesubstrate 530 b is formed based on a sphere of radius r′, where r>r′.Usually the surface modifications will be found beneath substantiallyall of the diamond table.

Referring to FIG. 13G, another generally spherical compact 535 is shownthat includes a diamond table 536 sintered to a substrate 536. Thesubstrate is configured as a sphere with a protruding cylindrical shape.The head 535 is formed so that a quantity of substrate protrudes fromthe spherical shape of the head to form a neck 538 which may be attachedto an appropriate body by any known attachment method. The use of a neck538 preformed on the substrate that is used to manufacture apolycrystalline diamond or cubic boron nitride compact 535 provides anattachment point on the polycrystalline diamond compact that may beutilized without disturbing the residual stress field of the compact.The neck 538 depicted is an integral component of a stem 540.

Any of the previously mentioned substrate configurations and substratetopographies and variations and derivatives of them may be used tomanufacture a polycrystalline diamond or polycrystalline cubic boronnitrode compact for use in a variety of fields. In various embodiments,a single layer substrate may be utilized. In other embodiments, atwo-layer substrate may be utilized, as discussed. Depending on theproperties of the components being used, however, it may be desired toutilize a substrate that includes three, four or more layers.

Segmented and Continuous Superhard Structures

In this section, the concept of structures which use segments of hard orsuperhard materials is discussed. The segments (or inserts) may presenta concave, convex or planar contact area, as desired, and can simplifyconstruction of products with complex geometries. Structures withsegmented superhard surfaces may be made by sintering the superhardsegments in place on a substrate so that the segments of superhardmaterial and the substrate form an integral superhard compact. Orstructures with segmented superhard or hard surfaces may be made bymanufacturing the superhard or hard material in advance, and theninstalling it in a separate substrate later by such techniques asfriction fit, interference fit, mechanical interlock, brazing, welding,adhesion, etc. For comparison, superhard structures with continuoussurfaces are also discussed below. Example segmented and continuousstructures are now discussed.

The geometry in FIGS. 4A-4B consists of veins or stripes of bearingmaterial that start from a polar region and migrate outward with aslight angular propensity. FIG. 4A illustrates a side view of the head4A-101. Specifically, the substrate material 4A-104 is marked byelevated ridges of diamond 4A-102 and recessed troughs 4A-103 betweenthe diamond ridges 4A-102. FIG. 4B is a top view of FIG. 4A illustratinga pattern of arcuate ridges emanating from a central location orspherical point. A straight-line version of this pattern is alsopossible.

The geometry of FIGS. 4C-4D consists of undulating lines that arecontinuous around the surface of the sphere. FIG. 4C illustrates a sideview of the head with a spherical point 4C-101 such that elevatednon-linear ridges of diamond 4C-103 wrap around the substrate material4C-102. Like FIGS. 4A and 4B, troughs 4C-104 exist between the diamondridges 4C-103. FIG. 4D is a top view of FIG. 4C. A straight line versionof this pattern is also possible.

Materials for the inserts include but are not limited to diamond, cubicboron nitride, corbonitride steels, steel, carbonitrides, borides,nitrides, silicides, carbides, ceramic matrix composites, fiberreinforced ceramic matrix composites, cast iron, carbon and alloysteels, stainless steel, roller bearing steel, tool steel, hard facingalloys, cobalt based alloys, Ni3Al alloys, surface treated titaniumalloys, cemented carbides, cermets, ceramics, carbon-graphite basedmaterials, fiber reinforced thermoplastics, metal matrix composites.

Materials for the substrate include but are not limited to corbonitridesteels, steel, carbonitrides, borides, nitrides, silicides, carbides,ceramic matrix composites, fiber reinforced ceramic matrix composites,cast iron, carbon and alloy steels, stainless steel, roller bearingsteel, tool steel, hard facing alloys, cobalt based alloys, Ni3Alalloys, surface treated titanium alloys, cemented carbides, cermets,ceramics, carbon-graphite based materials, fiber reinforcedthermoplastics, metal matrix composites.

The substrate may be configured such as to place the insert materialinto a compressive state sufficient to impart structural stability tothe insert material that heretofore was not present. The insert materialis put into a compressive state by the use of an interference fit withthe surrounding substrate material. By placing the insert material inthis compressive condition the neutral stress axis in the insertmaterial is displaced in such a fashion that the bearing material is nowcapable of sustaining higher loading while maintaining its structuralintegrity in combination with its superior wear properties. This allowsfor the use of materials that have very desirable wear properties butinsufficient structural capacity to now be configured in such a manneras to make them candidates for wear bearings that heretofore notavailable for use. The substrate material may be machined or cast withthe desired geometry for the bearing material. The substrate material isthen heated to a pre-determined temperature and the wear bearing insertsare cooled to a pre-determined temperature and then the wear bearinginsert is pressed into the substrate. The difference in size of thematerials results in the wear bearing material being in a compressivestate.

FIGS. 4E and 4E-1 depict a spherical structure 4E109 with a continuoussuperhard surface. The structure 4E109 depicted may be a polycrystallinediamond compact that includes a surface volume of diamond 4E9 on asubstrate 4E10. This embodiment includes a continuous surface layer ofdiamond, although the diamond surface may be discontinuous as well.

FIGS. 4F and 4F1 depict a segmented ball 4F110 with superhard inserts4F11 on the surface 4F12 to form a discontinuous superhard surface. Theinserts 4F11 may be located on the substrate material with greatprecision and accuracy. The surface of the ball may be divided intoareas of diamond or other superhard material separate by veins ofsubstrate material. Fabrication of balls with this vein and patchstructure (such as a polyhedral or round segmented surface) offer someadvantages to the manufacturing process for certain substrate metals aswell as provide some advantages in high impact situations. Each bearingsegment of diamond or superhard material independently accomodatetransient deformations under peak load without resulting in fracture ofthe segments of diamond or superhard material.

FIGS. 4G and 4G1 depict a cross-sectional view of a ball 4G111 withplugs 4G 14. The plugs 4G 14 may be a polycrystalline diamond compacthaving a surface of polycrystalline diamond or other superhard material.The plugs 4G14 may be fixed securely into receptacles on sphericalsubstrate ball 4G 15 or other desired structure, or they may be formedas a compact with the substrate. The plugs or segments may be fashionedas polycrystalline diamond compacts or other superhard material. Eachplug may be a continuous phase of superhard material, or a compactformed from a bearing surface of superhard material on a substrate, suchas a polycrystalline diamond compact. The plugs may be bonded, welded,or mechanically fastened to the substrate structure, preferably in anappropriate receptacle, leaving a superhard bearing surface exposed.High quality curvilinear and spherical surface finishes that areobtained by terminal finishing processes described later in thisdocument. This approach to segmented bearing surfaces permits thefabrication of extremely large spherical and or curvilinear bearingsurfaces not possible with continuous bearing surfaces. Size limitationsin the manufacturing of polycrystalline diamond compact elements mightotherwise prevent manufacture of such large elements.

FIGS. 4H and 4H1 depict a ball 4H112 constructed of solid or continuousphase polycrystalline diamond or other superhard material. This ball4H112 is made of solid diamond or superhard material without a separatesubstrate. The ball 4H112 has a continuous phase of diamond throughoutits interior. Embodiments of such a continuous phase bearing element maybe made from polycrystalline diamond, polycrystalline cubic boronnitride, or other superhard material. This structure has certainadvantages from a chemical electromagnetic and structural standpoint.

FIGS. 4I and 4I1 depict a ball 4I113 with strips, veins or adiscontinuous pattern of diamond 4I17 or another superhard materiallocated on a substrate 4I18. The diamond on the ball 4I113 surface maybe in a regular or irregular discontinuous pattern in any desiredgeometry, such a concentric circles, spirals, latitudinal orlongitudinal lines or otherwise. This structure possesses some of theadvantages common to the segmented bearing surface described above.

Finishing Methods and Apparatuses.

Once a PDC has been sintered, a mechanical finishing process may beemployed to prepare the final product. The finishing steps explainedbelow are described with respect to finishing a PDC, but they could beused to finish any other surface or any other type of component.

The synthetic diamond industry was faced with the problem of finishingflat surfaces and thin edges of diamond compacts. Methods for removal oflarge amounts of diamond from non-planar surfaces or finishing thosesurfaces to high degrees of accuracy for sphericity, size and surfacefinish had not been developed in the prior art.

Finishing of Superhard Cylindrical and Flat Forms.

In order to provide a greater perspective on finishing techniques forcurved and non-planar superhard surfaces for modular bearing inserts andjoints, a description of other finishing techniques is provided.

Lapping.

A wet slurry of diamond grit on cast iron or copper rotating plates areused to remove material on larger flat surfaces (e.g., up to about 70mm. in diameter). End coated cylinders of size ranging from about 3 mmto about 70 mm may also be lapped to create flat surfaces. Lapping isgenerally slow and not dimensionally controllable for depth and layerthickness, although flatness and surface finishes can be held to veryclose tolerances.

Grinding.

Diamond impregnated grinding wheels are used to shape cylindrical andflat surfaces. Grinding wheels are usually resin bonded in a variety ofdifferent shapes depending on the type of material removal required(i.e., cylindrical centerless grinding or edge grinding). PDCs aredifficult to grind, and large PDC surfaces are nearly impossible togrind. Consequently, it is desirable to keep grinding to a minimum, andgrinding is usually confined to a narrow edge or perimeter or to thesharpening of a sized PDC end-coated cylinder or machine tool insert.

Electro Spark Discharge Grinding (EDG).

Rough machining of PDC may be accomplished with electro spark dischargegrinding (“EDG”) on large diameter (e.g., up to about 70 mm.) flatsurfaces. This technology typically involves the use of a rotatingcarbon wheel with a positive electrical current running against a PDCflat surface with a negative electrical potential. The automaticcontrols of the EDG machine maintain proper electrical erosion of thePDC material by controlling variables such as spark frequency, voltageand others. EDG is typically a more efficient method for removing largervolumes of diamond than lapping or grinding. After EDG, the surface mustbe finish lapped or ground to remove what is referred to as the heataffected area or re-cast layer left by EDG.

Wire Electrical Discharge Machining (WEDM).

WEDM is used to cut superhard parts of various shapes and sizes fromlarger cylinders or flat pieces. Typically, cutting tips and inserts formachine tools and re-shaping cutters for oil well drilling bitsrepresent the greatest use for WEDM in PDC finishing.

Polishing.

Polishing superhard surfaces for modular bearing inserts and joints tovery high tolerances may be accomplished by diamond impregnated highspeed polishing machines. The combination of high speed and highfriction temperatures tends to burnish a PDC surface finished by thismethod, while maintaining high degrees of flatness, thereby producing amirror-like appearance with precise dimensional accuracy.

Finishing a Non-Planar Geometry.

Finishing a non-planar surface (concave non-planar or convex non-planar)presents a greater problem than finishing a flat surface or the roundededge of a cylinder. The total surface area of a sphere to be finishedcompared to the total surface area of a round end of a cylinder of likeradius is four (4) times greater, resulting in the need to remove four(4) times the amount of PDC material. The nature of a non-planar surfacemakes traditional processing techniques such as lapping, grinding andothers unusable because they are adapted to flat and cylindricalsurfaces. The contact point on a sphere should be a point contact thatis tangential to the edge of the sphere, resulting in a smaller amountof material removed per unit of time, and a proportional increase infinishing time required. Also, the design and types of processingequipment and tooling required for finishing non-planar objects must bemore accurate and must function to closer tolerances than those forother shapes. Non-planar finishing equipment also requires greaterdegrees of adjustment for positioning the work piece and tool ingressand egress.

The following are steps that may be performed in order to finish anon-planar, rounded or arcuate surface.

1.) Rough Machining.

Initially rough out the dimensions of the surface using a specializedelectrical discharge machining apparatus may be performed. FIG. 38depicts roughing a PDC sphere 3803. A rotator 3802 is provided that iscontinuously rotatable about its longitudinal axis (the z axisdepicted). The sphere 3803 to be roughed is attached to a spindle of therotator 3802. An electrode 3801 is provided with a contact end 3801 athat is shaped to accommodate the part to be roughed. In this case thecontact end 3801 a has a partially non-planar shape. The electrode 3801is rotated continuously about its longitudinal axis (the y axisdepicted). Angular orientation of the longitudinal axis y of theelectrode 3801 with respect to the longitudinal axis z of the rotator3802 at a desired angle β is adjusted to cause the electrode 3801 toremove material from the entire non-planar surface of the ball 3803 asdesired.

Thus, the electrode 3801 and the sphere 3803 are rotating aboutdifferent axes. Adjustment of the axes can be used to achieve nearperfect non-planar movement of the part to be roughed. Consequently, anearly perfect non-planar part results from this process. This methodproduces PDC non-planar surfaces with a high degree of sphericity andcut to very close tolerances. By controlling the amount of currentintroduced to the erosion process, the depth and amount of the heataffected zone can be minimized.

In the case of a PDC, the heat affected zone can be kept to about 3 to 5microns in depth and is easily removed by grinding and polishing withdiamond impregnated grinding and polishing wheels.

Referring to FIG. 39, roughing a convex non-planar PDC 3903 such as anacetablular cup is depicted. A rotator 3902 is provided that iscontinuously rotatable about its longitudinal axis (the z axisdepicted). The part 3903 to be roughed is attached to a spindle of therotator. An electrode 3901 is provided with a contact end 3901 a that isshaped to accommodate the part to be roughed. The electrode 3901 iscontinuously rotatable about its longitudinal axis (the y axisdepicted). Angular orientation of the longitudinal axis y of theelectrode 3901 with respect to the longitudinal axis z of the rotator3902 at a desired angle β is adjusted to cause the electrode 3901 toremove material from the entire non-planar surface of the cup 3903 asdesired.

In some embodiments, multiple electro discharge machine electrodes willbe used in succession in order to machine a part. A battery of electrodischarge machines may be employed to carry this out in assembly linefashion. Further refinements to machining processes and apparatuses aredescribed below.

Complex positive or negative relief (concave or convex) forms can bemachined into PDC or PCBN parts. This is a standard Electrical DischargeMachining (EDM) CNC machining center and suitably machined electrodesaccomplish the desired forms.

FIG. 40 (side view) and FIG. 40 a (end view) show an electrode 4001 witha convex form 4002 machined on the active end of the electrode 4001, andthe electrode base 4005. FIG. 41 (cross section at 41-41) and FIG. 41 ashow an electrode 4101 with a concave form 4102 and base 4105. Theopposite ends of the electrodes are provided with an attachmentmechanism at the base 4105 suitable for the particular EDM machine beingutilized.

There are a variety of electrode materials that can be utilized such acopper, copper tungsten, graphite, and combinations of graphite andmetal mixes. Materials best suited for machining PDC and PCBN are coppertungsten for roughing and pure graphite, or graphite copper tungstenmixes. Not all EDM machines are capable of machining PDC and PCBN. Onlythose equipped with capacitor discharge power supplies can generatespark intensities with enough power to efficiently erode thesematerials.

The actual size of the machined relief form is usually machinedundersized to allow for a suitable spark gap for the burning/erosionprocess to take place. Each spark gap length dictates a set of machiningparameters that must be set by the machine operator to ensure efficientelectrical discharge erosion of the material to be removed. Normally,two to four electrodes are prepared with different spark gap allowances.For example, an electrode using a 0.006 In. spark gap could be preparedfor “roughing,” and an “interim” electrode at 0.002 In. spark gap, and“finishing” electrode at 0.0005 In. spark gap. In each case themachining voltage (V), peak amperage (AP), pulse duration (P), referencefrequency (RF), retract duration (R), under-the-cut duration (U), andservo voltage (SV) must be set up within the machines control system.

FIG. 42 shows an EDM relief form 4201 sinking operation in a PDC insertpart 4202. Table 39 describes the settings for using a copper tungstenelectrode 4203 for roughing and a graphite/copper tungsten electrode forfinishing. The spark gap 4204 is also depicted.

TABLE 39 Electrode Spark Gap 4203 4204 V AP P RF Roughing .006 −2 7 1356 Finishing .001 −5 4 2 60

Those familiar with the field of EDM will recognize that variations inthe parameters shown will be required based on the electrodeconfiguration, electrode wear rates desired, and surface finishesrequired. Generally, higher machining rates, i.e., higher values of “V”and “AP” produce higher rates of discharge erosion, but converselyrougher surface finishes.

Obtaining very smooth and accurate finishes also requires the use of aproper dielectric machining fluid. Synthetic hydrocarbons with satelliteelectrodes as disclosed in U.S. Pat. No. 5,773,782, which is herebyincorporated by reference, appear to assist in obtaining high qualitysurface finishes.

FIG. 43 shows an embodiment wherein a single ball-nosed (sphericalradiused) EDM electrode 4301 is used to form a concave relief form 4303in a PDC or PCBN part 4302. The electrode 4301 is plunged verticallyinto the part 4302 and then moved laterally to accomplish the rest ofthe desired shape. By programming a CNC system EDM electrode “cuttingpath” of the EDM machine, an infinite variety of concave or convexshapes can be machined. Controlling the rate of “down” plunging and“lateral” cross cutting, and using the correct EDM material will dictatethe quality of the size dimensions and surface finishes obtained.

2.) Finish Grinding and Polishing.

Once the non-planar surface (whether concave or convex) has been roughmachined as described above or by other methods, finish grinding andpolishing of a part can take place. Grinding is intended to remove theheat affected zone in the PDC material left behind by electrodes.

In some embodiments of the devices, grinding utilizes a grit sizeranging from 100 to 150 according to standard ANSI B74.16-1971 andpolishing utilizes a grit size ranging from 240 to 1500, although gritsize may be selected according to the user's preference. Wheel speed forgrinding should be adjusted by the user to achieve a favorable materialremoval rate, depending on grit size and the material being ground. Asmall amount of experimentation can be used to determine appropriatewheel speed for grinding. Once the spherical surface (whether concave orconvex) has been rough machined as described above or by other methods,finish grinding and polishing of a part can take place. Grinding isintended to remove the heat affected zone in the PDC material leftbehind by electrodes. Use of the same rotational geometry as depicted inFIGS. 38 and 39 allows sphericity of the part to be maintained whileimproving its surface finish characteristics.

Referring to FIG. 44, it can be seen that a rotator 4401 holds a part tobe finished 4403, in this case a convex sphere, by use of a spindle. Therotator 4401 is rotated continuously about its longitudinal axis (the zaxis). A grinding or polishing wheel 4402 is rotated continuously aboutits longitudinal axis (the x axis). The moving part 4403 is contactedwith the moving grinding or polishing wheel 4402. The angularorientation β of the rotator 4401 with respect to the grinding orpolishing wheel 4402 may be adjusted and oscillated to effect grindingor polishing of the part (ball or socket) across its entire surface andto maintain sphericity.

Referring to FIG. 45, it can be seen that a rotator 4501 holds a part tobe finished 4503, in this case a convex non-planar cup, by use of aspindle. The rotator 4501 is rotated continuously about its longitudinalaxis (the z axis). A grinding or polishing wheel 4502 is provided thatis continuously rotatable about its longitudinal axis (the x axis). Themoving part 4503 is contacted with the moving grinding or polishingwheel 4502. The angular orientation β of the rotator 4501 with respectto the grinding or polishing wheel 4502 may be adjusted and oscillatedif required to effect grinding or polishing of the part across thenon-planar portion of it surface.

In one embodiment, grinding utilizes a grit size ranging from 100 to 150according to standard ANSI B74.16-1971 and polishing utilizes a gritsize ranging from 240 to 1500, although grit size may be selectedaccording to the user's preference. Wheel speed for grinding should beadjusted by the user to achieve a favorable material removal rate,depending on grit size and the material being ground. A small amount ofexperimentation can be used to determine appropriate wheel speed forgrinding.

As desired, a diamond abrasive hollow grill may be used for polishingdiamond or superhard surfaces. A diamond abrasive hollow grill includesa hollow tube with a diamond matrix of metal, ceramic and resin(polymer).

If a diamond surface is being polished, then the wheel speed forpolishing will be adjusted to cause a temperature increase or heatbuildup on the diamond surface. This heat buildup will cause burnishingof the diamond crystals to create a very smooth and mirror-like lowfriction surface. Actual material removal during polishing of diamond isnot as important as removal of sub-micron sized asperities in thesurface by a high temperature burnishing action of diamond particlesrubbing against each other. A surface speed of 6000 feet per minuteminimum is generally required together with a high degree of pressure tocarry out burnishing. Surface speeds of 4000 to 10,000 feet per minuteare believed to be the most desirable range. Depending on pressureapplied to the diamond being polished, polishing may be carried out atfrom about 500 linear feet per minute and 20,000 linear feet per minute.

Pressure must be applied to the work piece to raise the temperature ofthe part being polished and thus to achieve the most desired mirror-likepolish, but temperature should not be increased to the point that itcauses complete degradation of the resin bond that holds the diamondpolishing wheel matrix together, or resin will be deposited on thediamond. Excessive heat will also unnecessarily degrade the surface ofthe diamond.

Maintaining a constant flow of coolant (such as water) across thediamond surface being polished, maintaining an appropriate wheel speedsuch as 6000 linear feet per minute, applying sufficient pressureagainst the diamond to cause heat buildup but not so much as to degradethe wheel or damage the diamond, and timing the polishing appropriatelyare all important and must all be determined and adjusted according tothe particular equipment being used and the particular part beingpolished. Generally the surface temperature of the diamond beingpolished should not be permitted to rise above 800 degrees Celsius orexcessive degradation of the diamond will occur. Desirable surfacefinishing of the diamond, called burnishing, generally occurs between650 and 750 degrees Celsius.

During polishing it is important to achieve a surface finish that hasthe lowest possible coefficient of friction, thereby providing a lowfriction and long-lasting, surface. Once a diamond or other superhardsurface is formed in modular bearing inserts and joints, the surface maythen be polished to an Ra value of 0.3 to 0.005 microns. Acceptablepolishing will include an Ra value in the range of 0.5 to 0.005 micronsor less. The parts of the modular bearing inserts and joints may bepolished individually before assembly or as a unit after assembly. Othermethods of polishing PDCs and other superhard materials may be adaptedto work with the invented modular bearing inserts and joints, with theobjective being to achieve a smooth surface, with an Ra value of0.01-0.005 microns. Further grinding and polishing details are providedbelow.

FIG. 46 shows a diamond grinding form 4601 mounted to an arbor 4602,which is in turn mounted into the high-speed spindle 4603 of a CNCgrinding machine. The cutting path motion 4604 of the grinding form 4601is controlled by the CNC program allowing the necessary surface coveragerequiring grinding or polishing. The spindle speed is generally relatedto the diameter of the grinding form and the surface speed desired atthe interface with the material 4605 to be removed. The surface speedshould range between 4,000 and 17,000 feet per minute for both grindingand polishing. For grinding, the basic grinding media for the grindingform should be as “free cutting” as practical with diamond grit sizes inthe range of 80 to 120 microns and concentrations ranging from 75 to125. For polishing the grinding media should not be as “free cutting,”i.e., the grinding form should generally be harder and denser with gritsizes ranging from 120 to 300 microns and concentrations ranging from100 to 150.

Superhard materials can be more readily removed by grinding if theactual area of the material being removed is kept as small as possible.Ideally the bruiting form 4601 should be rotated to create conditions inthe range from 20,000 to 40,000 surface feet per minute between the part4605 and the bruiting form 4601. Spindle pressure between the part 4605and the bruiting form 4601 operating in a range of 10 to 100 Lbs—forceproducing an interface temperature between 650 and 750 degrees Celsiusis required. Cooling water is needed to take away excess heat to keepthe part from possibly failing. The simplest way to keep the grind areasmall is to utilize a small cylindrical contact point (usually a ballform, although a radiused end of a cylinder accomplishes the samepurpose), operating against a larger surface area.

FIG. 47 shows the tangential area of contact 4620 between the grindingform 4601 and the substantially larger superhard material 4621. Bycontrolling the path of the grinding form cutter, small grooves 4630(FIG. 48) can be ground into the surface of the superhard material 4621removing the material and leaving small “cusps” 4640 between theadjacent grooves. As the grooves are cut shallower and closer togetherthe “cusps” 4640 become imperceptible to the naked eye and are easilyremoved by subsequent polishing operations. The cutter line path of thegrinding form cutter should be controlled by programming the CNC systemof the grinding machine to optimize the cusp size, grinding form cutterwear, and material removal rates.

Bruiting.

Obtaining highly polished surface finishes on PDC, PBCN, and othersuperhard materials in the range of 0.05 to 0.005 μm can be obtained byrunning a PDC form against the surface to be polished. “Bruiting” orrubbing a diamond surface under high pressure and temperature againstanother superhard material degredates or burns away any positiveasperities remaining from previous grinding and polishing operationsproducing a surface finish not obtainable in any other way.

FIG. 49 shows a PDC dome part 4901 on a holder 4904 and being “BruitPolished” using a PDC bruiting form 4902 being rotated in a high-speedspindle 4903. Ideally the bruiting form should be rotated in a rangefrom 20,000 to 40,000 surface feet per minute with the spindle pressureoperating in a range of 10 to 100 Lbs—force producing an interfacetemperature between 650 and 750 degrees Celsius. Angle α 4905 representsthe angular orientation of the longitudinal axis of the spindle 4903with respect to the central axis of the part 4901. Cooling water isgenerally required to take away excess heat to keep the part fromfailing.

FIG. 50 shows another embodiment of the bruiting polishing techniquewherein the PDC bruiting form 5001 is controlled through a complexsurface path 5002 by a CNC system of a grinding machine or a CNC Millequipped with a high-speed spindle to control the point of contact 5003of the form 5001 with a superhard component 5004.

Use of Cobalt Chrome Molybdenum (CoCrMo) Alloys to AugmentBiocompatibility in PDCS.

Cobalt and Nickel may be used as catalyst metals for sintering diamondpowder to produce sintered PDCs. The toxicity of both Co and Ni is welldocumented; however, use of CoCr alloys which contain Co and Ni haveoutstanding corrosion resistance and avoid passing on the toxic effectsof Co or Ni alone. Use of CoCrMo alloy as a solvent-catalyst metal inthe making of sintered PDCs yields a biocompatible and corrosionresistant material. Such alloys may be defined as any suitablebiocompatible combination of the following metals: Co, Cr, Ni, Mo, Tiand W. Examples include ASTM F-75, F-799 and F-90. Each of these willserve as a solvent-catalyst metal when sintering diamond. Elementalanalysis of the interstitial metal in PDC made with these alloys hasshown that the composition is substantially more corrosion resistantthan PDC made with Co or Ni alone. Interstitial metal in PDC made withthese metals is substantially more corrosion resistant than PDC madewith Co or Ni is and is therefore well suited for medical applications.

Carbides as Substrate Materials

Following known procedures for the production of carbides, both Ti/TiC(Ti cemented TiC) and Nb/TiC (Nb cemented TiC) can be manufactured foruse as substrate materials in prosthetic joints (such as femoral headsof prosthetic hip joints) and components thereof. Ti (or Nb) is mixedwith TiC powder and formed into a ball enclosed by an Nb can. Thematerials are then formed into a solid hipping (hot isostatic pressing)in a high pressure press. The result is either Ti cemented TiC or Nbcemented TiC, producing a biocompatabile product. The same result couldalso be achieved by sintering the Ti (or Nb)+TiC using known sinteringprocedures such as those used in the carbide industry. Ti, Nb and TiChave biocompatible materials and therefore can be used for biomedicalapplications such as spinal and hip implants among others.

Carbide and metal micron powders are added together in a container withwax and acetone or other appropriate solvent along with carbide mixingballs. The materials are then milled in an attritor mill for examplesfor an appropriate period of time to thoroughly mix all components andto reduce the material to the target grain size (the process iscontrolled to obtain a specific grain size). After milling the solventis evaporated off and the resulting powder is then pressed in acompaction press to the desired shape. The individual parts are thenplaced in a furnace and slowly heated to burn off the wax. Too rapid awax removal will cause the parts to have excessive porosity or causethem to catastrophically fall apart. After removal of the wax, the partsare then taken up to the sintering temperature and held until sinteringis complete. To minimize or completely eliminate open porosity, theparts may be hipped in a standard hipping furnace in which the parts arepressurized to ˜30,000 psi. A more extreme hipping process is alsoavailable called rapid omnidirectional compaction (ROC). In this processthe parts are rapped in grafoil or graphite paper and placed in apressure container with glass powder. The contents are then taken to125,000 psi and the target temperature where the glass powder melts atwhich time it uniformly applies pressure to the part, thus essentiallyreducing the porosity to zero.

The actual temperature for sintering carbides is determined by thesystem that one is working in. For tungsten carbide the temperature isapproximately 1200° C. A typical hipping pressure is 30,000 psi whereasin the ROC process it is ˜125,000 psi. The target temperature andpressure are approached slowly over several hours. When the targetconditions are attained they are held for only minutes before thepressure and temperature are slowly decreased to room temperature andpressure.

Material formulations for carbides is determined by the ultimate use ofthe material. If toughness is the desired property then the metalcontent of the carbide will range upwards of 13 to >20 weight %. If wearresistance or a low thermal expansion are the desired properties thenthe metal content of the carbide will be <13 weight %.

Use of Ti and Nb Cemented TiC for use in Prosthetic Joints

A sintering and/or hipping process can be used to create Ti or Nbcemented TiC balls. The balls are then placed in an Nb can with diamondbetween the can and the ball. The filled can is then placed in a highpressure/high temperature press and the diamond is sintered to the ball.Ti and Nb are useful in this ball production process because diamondwill chemically bond with TiC grains during the sintering process in astructure that is similar to the crystalline structure of diamond. Thediamond will also chemically bond to the Ti and Nb because both are goodcarbide forming elements. The chemical bonding will increase theadhesion of the diamond to the substrate (ball core) and prevent thediamond from delaminating during use. Ti and Nb are used in conjunctionwith TiC because their dilatation during the sintering process exceedsthat of their coefficient of thermal expansion (CTE), consequently astrong ball that does not suffer fracture from residual stress isproduced. The balance between the material properties of the diamondlayer and the core ball or substrate is accomplished by calculating thevolumetric thermal expansion of all components (=3*CTE*ΔT, where ΔT isthe temperature difference between room temperature and the sinteringtemperature). Similarly the volumetric dilatation must be calculated forall components using the following equation, (−3*p*(1−ν))/E; where p isthe sintering pressure, ν is Poisson's ratio and E is the elasticmodulus. The CTE and the dilatation are then added together for eachcomponent. The resulting values for each of the components in thediamond layer are then multiplied by their respective volumetric ratioin the diamond layer (the volumetric ratio of diamond to metal isfixed). These two numbers, one for the diamond and one for the metal,when added together is the total volumetric change that will occur oncoming down from high pressure/temperature to room temperature for thediamond table. The is the volumetric change that must be matched by thecore. To find this volume, multiply the combined CTE/dilatation for eachof the two components in the core, Ti and TiC, for example by variousratios (must add to 1) until the result equals the volumetric change ofthe diamond layer. Only the change occurring from hightemperature/pressure to room temperature/pressure is considered becauseat the sintering conditions the diamond will sinter around the once ithas fully expanded and dilitated. Thus there will be no residual stressbetween them at the sintering conditions. By balancing the volumetricchanges between the core and the diamond layer, they will both undergothe same volumetric changes on cooling and depressurization resulting inlittle or no residual stress at room temperature/pressure conditions.

While the present devices, components thereof, materials therefore, andmanufacturing methods have been described and illustrated in conjunctionwith a number of specific configurations, those skilled in the art willappreciate that variations and modifications may be made withoutdeparting from the principles herein illustrated, described, andclaimed. The present invention, as defined by the appended claims, maybe embodied in other specific forms without departing from its spirit oressential characteristics. The configurations described herein are to beconsidered in all respects as only illustrative, and not restrictive.All changes which come within the meaning and range of equivalency ofthe claims are to be embraced within their scope.

1. A method for making a sintered superhard prosthetic joint componentcomprising: obtaining a cemented TiC substrate, said substratecomprising TiC which is cemented with a carbide forming agent selectedfrom the group consisting of Ti, Nb and a combination of Ti and Nb,placing a diamond table adjacent at least a portion of said substrate,said substrate and said diamond table being configured to achieve ashape and dimension desirable for use in a prosthetic joint component,and placing said substrate and diamond table in a press and exposingsaid substrate and diamond table to high pressure and high temperaturein order to cause sintering of said diamond table and said substrate inorder to form a sintered polycrystalline diamond compact joint componentthat includes a diamond table on a substrate.
 2. A method as recited inclaim 1 wherein said carbide forming agent chemically bonds with TiCduring said sintering step.
 3. A method as recited in claim 2 whereinsaid carbide forming agent bonded to said TiC has a structure similar tothe crystalline structure of diamond.
 4. A method as recited in claim 1wherein said diamond chemically bonds to said carbide forming agent. 5.A method as recited in claim 1 wherein said substrate is spherical.
 6. Amethod as recited in claim 1 wherein said sintered polycrystallinediamond compact joint component is spherical in shape.
 7. A method asrecited in claim 1 wherein said sintered polycrystalline diamond compactjoint component diamond table has an exterior surface at least a portionof which is non-planar.
 8. A method as recited in claim 1 wherein saidcarbide forming agent includes both Ti and Nb.
 9. A method as recited inclaim 1 wherein said carbide forming agent experiences dilatation duringsintering that exceeds its coefficient of thermal expansion.
 10. Amethod as recited in claim 9 wherein said sintered polycrystallinediamond compact joint component is free from fracture caused by residualstress.
 11. A method as recited in claim 1 further comprising the stepof achieving a balance of volumetric thermal expansion and volumetricdilatation in each of said substrate and said diamond in order tominimize differences in volumetric expansion between said substrate andsaid diamond.
 12. A method as recited in claim 1 wherein the volumetricchange of said diamond during cooling and reduction of pressure aftersintering is substantially the same as the volumetric change of saidsubstrate during cooling and reduction of pressure after sintering. 13.A method as recited in claim 12 wherein said component is substantiallyfree from residual stress.
 14. A method as recited in claim 1 whereinthe method comprises placing the substrate and diamond table in arefractory metal can prior to said sintering step, and wherein said canincludes Nb.
 15. A method for making a sintered superhard prostheticjoint component comprising: obtaining a cemented TiC substrate ball,said ball being cemented with a carbide forming agent selected from thegroup consisting of Ti, Nb and combinations of Ti and Nb, placing saidsubstrate in a can with diamond between said can and said ball, andplacing said can in a press and exposing said can and its contents tohigh pressure and high temperature in order form a joint component thatincludes a diamond table on a substrate.
 16. A method as recited inclaim 15 wherein said press carries out a sintering step on said balland said diamond.
 17. A method as recited in claim 15 wherein said presscarries out a hipping step on said ball and said diamond.
 18. A methodas recited in claim 15 wherein said carbide forming agent chemicallybonds with TiC in said press.
 19. A method as recited in claim 15wherein said carbide forming agent bonds to said TiC in said press toform a structure similar to the crystalline structure of diamond.
 20. Amethod as recited in claim 15 wherein said diamond chemically bonds tosaid carbide forming agent in said press.
 21. A method as recited inclaim 15 wherein said joint component is spherical in shape.
 22. Amethod as recited in claim 15 wherein said joint component diamond tablehas an exterior surface at least a portion of which is non-planar.
 23. Amethod as recited in claim 15 wherein said carbide forming agentincludes both Ti and Nb.
 24. A method as recited in claim 15 whereinsaid carbide forming agent experiences dilatation in said press thatexceeds its coefficient of thermal expansion.
 25. A method as recited inclaim 15 wherein said prosthetic joint component component is free fromfracture caused by residual stress.
 26. A method as recited in claim 15further comprising the step of achieving a balance of volumetric thermalexpansion and volumetric dilatation in each of said substrate and saiddiamond in order to minimize differenced in the volumetric expansion orcontraction between said substrate and said diamond upon cooling andreduction of pressure after sintering of the prosthetic joint.
 27. Amethod as recited in claim 15 wherein the volumetric change of saiddiamond during cooling and reduction of pressure after sintering issubstantially the same as the volumetric change of said substrate duringcooling and reduction of pressure after sintering.
 28. A method formaking a sintered superhard prosthetic joint component comprising:forming a prosthetic joint, the joint including: a substrate comprisinga carbide and a carbide forming agent selected from the group consistingof Ti, Nb, and mixtures of Ti and Nb; and a layer of diamond particlesplaced adjacent the substrate; and wherein the substrate and the diamondlayer are configured to achieve a shape and dimension desirable for usein a prosthetic joint component, and placing the prosthetic joint in apress and exposing the joint to high pressure and high temperature inorder to cause sintering of the diamond and the substrate in order toform a sintered polycrystalline diamond compact joint component thatincludes a diamond table on a substrate.
 29. The method of claim 28,wherein the method further comprises selecting a substrate comprisingTiC and carbide forming agent selected from the group consisting of Ti,Nb, and mixtures of Ti and Nb.
 30. The method of claim 28, wherein themethod further comprises selecting a substrate which is sintered priorto placing the diamond layer adjacent the substrate.
 31. The method ofclaim 28, wherein the method further comprises placing the substrate anddiamond layer in a metal can before sintering the prosthetic joint. 32.The method of claim 31, wherein the metal can is formed form Nb.
 33. Themethod of claim 28, wherein the sintering of the prosthetic joint causesbonding of the diamond to the carbide and to the at least one carbideforming agent in the substrate.
 34. The method of claim 28, wherein atleast a portion of the diamond layer of the prosthetic joint forms anon-planar articulation surface useful for articulation of the resultingprosthetic joint.
 35. The method of claim 28, wherein the composition ofthe substrate and the composition of the diamond layer are selected suchthat the ratio of volumetric change in the diamond layer when reducingthe temperature and pressure after sintering is equal to the ratio ofvolumetric change in the substrate when reducing the temperature andpressure after sintering, the ratio of volumetric change comprising thevolumetric thermal expansion and the dilatation due to pressure change.36. A method for forming a prosthetic joint comprising: forming a firstjoint component by: forming a substrate, the substrate comprising amixture of a carbide and a carbide forming element selected from thegroup consisting of Ti, Nb, and mixtures of Ti and Nb; forming a diamondtable adjacent the substrate; and sintering the diamond table to thesubstrate under high pressure and temperature; wherein the diamond tableis shaped to form a first articulation surface on the surface of thediamond table; forming a second joint component by: forming a substrate,the substrate comprising a mixture of a carbide and a carbide formingelement selected from the group consisting of Ti, Nb, and mixtures of Tiand Nb; forming a diamond table adjacent the substrate; and sinteringthe diamond table to the substrate under high pressure and temperature;wherein the diamond table is shaped to form a second articulationsurface on the surface of the diamond table; and wherein the firstarticulation surface is configured for sliding interaction with thesecond articulation surface so as to provide articulation of theprosthetic joint.
 37. The method of claim 36, wherein the carbide in thesubstrates comprises TiC.
 38. The method of claim 36, wherein, for eachof the first and second joint components, the method comprises selectingthe composition of the substrate and the composition of the diamondtable such that the ratio of volumetric change in the diamond table whenreducing the temperature and pressure after sintering is approximatelyequal to the ratio of volumetric change in the substrate when reducingthe temperature and pressure after sintering, the ratio of volumetricchange comprising the volumetric thermal expansion and the dilatationdue to pressure change.
 39. The method of claim 36,wherein the first andsecond articulation surfaces comprise non-planar surfaces.